## Step 1: Define the symbolic representation of the problem
First, let's define the symbolic variables and the objective function based on the given problem description.

Let:
- $x_1$ represent 'milligrams of vitamin B6'
- $x_2$ represent 'milligrams of zinc'
- $x_3$ represent 'grams of fat'

The objective function to maximize is:
\[ 9x_1x_2 + 5x_1x_3 + 6x_2^2 + 2x_2x_3 + x_3^2 + 6x_1 + 3x_2 + 9x_3 \]

## Step 2: List the constraints
Constraints given:
1. $3x_1 \leq 71$
2. $11x_1 \leq 85$
3. $9x_1 \leq 64$
4. $3x_1 \leq 50$
5. $6x_2 \leq 71$
6. $5x_2 \leq 85$
7. $10x_2 \leq 64$
8. $8x_2 \leq 50$
9. $6x_3 \leq 71$
10. $9x_3 \leq 85$
11. $6x_3 \leq 64$
12. $4x_3 \leq 50$
13. $3x_1^2 + 6x_2^2 + 6x_3^2 \geq 17$
14. $9x_1^2 + 10x_2^2 \geq 13$
15. $8x_2 + 4x_3 \geq 13$
16. $3x_1 + 8x_2 + 4x_3 \geq 8$
17. $3x_1^2 + 6x_3^2 \leq 39$
18. $6x_2 + 6x_3 \leq 50$
19. $3x_1 + 6x_2 + 6x_3 \leq 50$
20. $11x_1 + 5x_2 \leq 69$
21. $5x_2 + 9x_3 \leq 52$
22. $11x_1^2 + 9x_3^2 \leq 42$
23. $11x_1 + 5x_2 + 9x_3 \leq 74$
24. $11x_1 + 5x_2 + 9x_3 \leq 74$
25. $9x_1 + 6x_3 \leq 21$
26. $9x_1 + 10x_2 \leq 61$
27. $9x_1 + 10x_2 + 6x_3 \leq 61$
28. $3x_1^2 + 4x_3^2 \leq 27$
29. $3x_1 + 8x_2 + 4x_3 \leq 27$

## Step 3: Convert the problem into a Gurobi code
We will use Gurobi to solve this optimization problem.

```python
import gurobi as gp

# Define the model
m = gp.Model("optimization_problem")

# Define the variables
x1 = m.addVar(name="milligrams_of_vitamin_B6", vtype=gp.GRB.INTEGER)
x2 = m.addVar(name="milligrams_of_zinc", vtype=gp.GRB.INTEGER)
x3 = m.addVar(name="grams_of_fat")

# Define the objective function
m.setObjective(9*x1*x2 + 5*x1*x3 + 6*x2**2 + 2*x2*x3 + x3**2 + 6*x1 + 3*x2 + 9*x3, gp.GRB.MAXIMIZE)

# Add constraints
m.addConstr(3*x1 <= 71)
m.addConstr(11*x1 <= 85)
m.addConstr(9*x1 <= 64)
m.addConstr(3*x1 <= 50)
m.addConstr(6*x2 <= 71)
m.addConstr(5*x2 <= 85)
m.addConstr(10*x2 <= 64)
m.addConstr(8*x2 <= 50)
m.addConstr(6*x3 <= 71)
m.addConstr(9*x3 <= 85)
m.addConstr(6*x3 <= 64)
m.addConstr(4*x3 <= 50)
m.addConstr(3*x1**2 + 6*x2**2 + 6*x3**2 >= 17)
m.addConstr(9*x1**2 + 10*x2**2 >= 13)
m.addConstr(8*x2 + 4*x3 >= 13)
m.addConstr(3*x1 + 8*x2 + 4*x3 >= 8)
m.addConstr(3*x1**2 + 6*x3**2 <= 39)
m.addConstr(6*x2 + 6*x3 <= 50)
m.addConstr(3*x1 + 6*x2 + 6*x3 <= 50)
m.addConstr(11*x1 + 5*x2 <= 69)
m.addConstr(5*x2 + 9*x3 <= 52)
m.addConstr(11*x1**2 + 9*x3**2 <= 42)
m.addConstr(11*x1 + 5*x2 + 9*x3 <= 74)
m.addConstr(11*x1 + 5*x2 + 9*x3 <= 74)
m.addConstr(9*x1 + 6*x3 <= 21)
m.addConstr(9*x1 + 10*x2 <= 61)
m.addConstr(9*x1 + 10*x2 + 6*x3 <= 61)
m.addConstr(3*x1**2 + 4*x3**2 <= 27)
m.addConstr(3*x1 + 8*x2 + 4*x3 <= 27)

# Solve the model
m.optimize()

# Print the solution
if m.status == gp.GRB.OPTIMAL:
    print("Optimal solution found.")
    print("Milligrams of vitamin B6: ", x1.varValue)
    print("Milligrams of zinc: ", x2.varValue)
    print("Grams of fat: ", x3.varValue)
    print("Objective function value: ", m.objVal)
else:
    print("No optimal solution found.")
```

## Step 4: Symbolic representation
The symbolic representation of the problem is as follows:

```json
{
    'sym_variables': [
        ('x1', 'milligrams of vitamin B6'),
        ('x2', 'milligrams of zinc'),
        ('x3', 'grams of fat')
    ],
    'objective_function': '9*x1*x2 + 5*x1*x3 + 6*x2^2 + 2*x2*x3 + x3^2 + 6*x1 + 3*x2 + 9*x3',
    'constraints': [
        '3*x1 <= 71',
        '11*x1 <= 85',
        '9*x1 <= 64',
        '3*x1 <= 50',
        '6*x2 <= 71',
        '5*x2 <= 85',
        '10*x2 <= 64',
        '8*x2 <= 50',
        '6*x3 <= 71',
        '9*x3 <= 85',
        '6*x3 <= 64',
        '4*x3 <= 50',
        '3*x1^2 + 6*x2^2 + 6*x3^2 >= 17',
        '9*x1^2 + 10*x2^2 >= 13',
        '8*x2 + 4*x3 >= 13',
        '3*x1 + 8*x2 + 4*x3 >= 8',
        '3*x1^2 + 6*x3^2 <= 39',
        '6*x2 + 6*x3 <= 50',
        '3*x1 + 6*x2 + 6*x3 <= 50',
        '11*x1 + 5*x2 <= 69',
        '5*x2 + 9*x3 <= 52',
        '11*x1^2 + 9*x3^2 <= 42',
        '11*x1 + 5*x2 + 9*x3 <= 74',
        '11*x1 + 5*x2 + 9*x3 <= 74',
        '9*x1 + 6*x3 <= 21',
        '9*x1 + 10*x2 <= 61',
        '9*x1 + 10*x2 + 6*x3 <= 61',
        '3*x1^2 + 4*x3^2 <= 27',
        '3*x1 + 8*x2 + 4*x3 <= 27'
    ]
}
```