## Step 1: Define the symbolic representation of the problem
The problem involves maximizing an objective function subject to several constraints. The variables are ['milkshakes', 'chicken thighs', 'oreos', 'granola bars'], which we can represent symbolically as ['x0', 'x1', 'x2', 'x3']. The objective function to maximize is $6 \cdot milkshakes + 2 \cdot chicken\ thighs + 8 \cdot oreos + 6 \cdot granola\ bars$, which translates to $6x_0 + 2x_1 + 8x_2 + 6x_3$.

## Step 2: List the constraints in symbolic notation
The constraints given are:
1. $4 \cdot milkshakes + 6 \cdot chicken\ thighs + 7 \cdot oreos + 6 \cdot granola\ bars \leq 144$ (protein constraint)
2. $9 \cdot milkshakes + 7 \cdot chicken\ thighs + 2 \cdot oreos + 10 \cdot granola\ bars \leq 134$ (cost constraint)
3. $6 \cdot chicken\ thighs + 6 \cdot granola\ bars \geq 36$ (protein from chicken thighs and granola bars)
4. $7 \cdot oreos + 6 \cdot granola\ bars \geq 36$ (protein from oreos and granola bars)
5. $4 \cdot milkshakes + 6 \cdot chicken\ thighs + 6 \cdot granola\ bars \geq 18$ (protein from milkshakes, chicken thighs, and granola bars)
6. $9 \cdot milkshakes + 10 \cdot granola\ bars \geq 25$ (minimum spend on milkshakes and granola bars)
7. $7 \cdot oreos + 6 \cdot granola\ bars \leq 88$ (max protein from oreos and granola bars)
8. $4 \cdot milkshakes + 6 \cdot granola\ bars \leq 131$ (max protein from milkshakes and granola bars)
9. $4 \cdot milkshakes + 6 \cdot chicken\ thighs \leq 116$ (max protein from milkshakes and chicken thighs)
10. $6 \cdot chicken\ thighs + 6 \cdot granola\ bars \leq 137$ (max protein from chicken thighs and granola bars)
11. $4 \cdot milkshakes + 6 \cdot chicken\ thighs + 7 \cdot oreos \leq 49$ (max protein from milkshakes, chicken thighs, and oreos)
12. $4 \cdot milkshakes + 7 \cdot oreos + 6 \cdot granola\ bars \leq 105$ (max protein from milkshakes, oreos, and granola bars)
13. $4 \cdot milkshakes + 6 \cdot chicken\ thighs + 7 \cdot oreos + 6 \cdot granola\ bars \leq 105$ (max protein from all)
14. $9 \cdot milkshakes + 10 \cdot granola\ bars \leq 40$ (max spend on milkshakes and granola bars)
15. $7 \cdot chicken\ thighs + 10 \cdot granola\ bars \leq 45$ (max spend on chicken thighs and granola bars)
16. $9 \cdot milkshakes + 2 \cdot oreos \leq 87$ (max spend on milkshakes and oreos)
17. $9 \cdot milkshakes + 2 \cdot oreos + 10 \cdot granola\ bars \leq 47$ (max spend on milkshakes, oreos, and granola bars)
18. $9 \cdot milkshakes + 7 \cdot chicken\ thighs + 2 \cdot oreos + 10 \cdot granola\ bars \leq 47$ (max spend on all)

## 3: Convert the problem into Gurobi code
```python
import gurobi

# Define the model
model = gurobi.Model()

# Define the variables
x0 = model.addVar(name="milkshakes", lb=0)
x1 = model.addVar(name="chicken_thighs", lb=0)
x2 = model.addVar(name="oreos", lb=0)
x3 = model.addVar(name="granola_bars", lb=0)

# Define the objective function
model.setObjective(6 * x0 + 2 * x1 + 8 * x2 + 6 * x3, gurobi.GRB.MAXIMIZE)

# Add constraints
model.addConstr(4 * x0 + 6 * x1 + 7 * x2 + 6 * x3 <= 144)  # protein constraint
model.addConstr(9 * x0 + 7 * x1 + 2 * x2 + 10 * x3 <= 134)  # cost constraint
model.addConstr(6 * x1 + 6 * x3 >= 36)  # protein from chicken thighs and granola bars
model.addConstr(7 * x2 + 6 * x3 >= 36)  # protein from oreos and granola bars
model.addConstr(4 * x0 + 6 * x1 + 6 * x3 >= 18)  # protein from milkshakes, chicken thighs, and granola bars
model.addConstr(9 * x0 + 10 * x3 >= 25)  # minimum spend on milkshakes and granola bars
model.addConstr(7 * x2 + 6 * x3 <= 88)  # max protein from oreos and granola bars
model.addConstr(4 * x0 + 6 * x3 <= 131)  # max protein from milkshakes and granola bars
model.addConstr(4 * x0 + 6 * x1 <= 116)  # max protein from milkshakes and chicken thighs
model.addConstr(6 * x1 + 6 * x3 <= 137)  # max protein from chicken thighs and granola bars
model.addConstr(4 * x0 + 6 * x1 + 7 * x2 <= 49)  # max protein from milkshakes, chicken thighs, and oreos
model.addConstr(4 * x0 + 7 * x2 + 6 * x3 <= 105)  # max protein from milkshakes, oreos, and granola bars
model.addConstr(4 * x0 + 6 * x1 + 7 * x2 + 6 * x3 <= 105)  # max protein from all
model.addConstr(9 * x0 + 10 * x3 <= 40)  # max spend on milkshakes and granola bars
model.addConstr(7 * x1 + 10 * x3 <= 45)  # max spend on chicken thighs and granola bars
model.addConstr(9 * x0 + 2 * x2 <= 87)  # max spend on milkshakes and oreos
model.addConstr(9 * x0 + 2 * x2 + 10 * x3 <= 47)  # max spend on milkshakes, oreos, and granola bars
model.addConstr(9 * x0 + 7 * x1 + 2 * x2 + 10 * x3 <= 47)  # max spend on all

# Optimize the model
model.optimize()

# Print the solution
if model.status == gurobi.GRB.OPTIMAL:
    print("Objective: ", model.objVal)
    print("Milkshakes: ", x0.x)
    print("Chicken Thighs: ", x1.x)
    print("Oreos: ", x2.x)
    print("Granola Bars: ", x3.x)
else:
    print("The model is infeasible")
```

## 4: Symbolic Representation
```json
{
    'sym_variables': [
        ('x0', 'milkshakes'), 
        ('x1', 'chicken thighs'), 
        ('x2', 'oreos'), 
        ('x3', 'granola bars')
    ], 
    'objective_function': '6*x0 + 2*x1 + 8*x2 + 6*x3', 
    'constraints': [
        '4*x0 + 6*x1 + 7*x2 + 6*x3 <= 144',
        '9*x0 + 7*x1 + 2*x2 + 10*x3 <= 134',
        '6*x1 + 6*x3 >= 36',
        '7*x2 + 6*x3 >= 36',
        '4*x0 + 6*x1 + 6*x3 >= 18',
        '9*x0 + 10*x3 >= 25',
        '7*x2 + 6*x3 <= 88',
        '4*x0 + 6*x3 <= 131',
        '4*x0 + 6*x1 <= 116',
        '6*x1 + 6*x3 <= 137',
        '4*x0 + 6*x1 + 7*x2 <= 49',
        '4*x0 + 7*x2 + 6*x3 <= 105',
        '4*x0 + 6*x1 + 7*x2 + 6*x3 <= 105',
        '9*x0 + 10*x3 <= 40',
        '7*x1 + 10*x3 <= 45',
        '9*x0 + 2*x2 <= 87',
        '9*x0 + 2*x2 + 10*x3 <= 47',
        '9*x0 + 7*x1 + 2*x2 + 10*x3 <= 47'
    ]
}
```