## Problem Description and Formulation

The problem requires maximizing the objective function:

\[ 6.04 \times \text{milligrams of vitamin B12} + 8.67 \times \text{milligrams of vitamin B4} + 8.34 \times \text{milligrams of vitamin C} \]

subject to several constraints related to the energy stability index.

## Constraints

1. The energy stability index of milligrams of vitamin B12 is 0.43.
2. The energy stability index for milligrams of vitamin B4 is 0.11.
3. The energy stability index of milligrams of vitamin C is 0.02.
4. The total combined energy stability index from milligrams of vitamin B12 and milligrams of vitamin B4 should be at least 21.
5. The total combined energy stability index from milligrams of vitamin B12 and milligrams of vitamin B4 should be at most 104.
6. The total combined energy stability index from milligrams of vitamin B12, milligrams of vitamin B4, and milligrams of vitamin C should be at most 104.

## Gurobi Code Formulation

```python
import gurobi

# Create a new model
model = gurobi.Model()

# Define variables
milligrams_vitamin_B12 = model.addVar(name="milligrams_vitamin_B12", lb=0)  # No upper bound given
milligrams_vitamin_B4 = model.addVar(name="milligrams_vitamin_B4", lb=0)  # No upper bound given
milligrams_vitamin_C = model.addVar(name="milligrams_vitamin_C", lb=0)  # No upper bound given

# Objective function
model.setObjective(6.04 * milligrams_vitamin_B12 + 8.67 * milligrams_vitamin_B4 + 8.34 * milligrams_vitamin_C, gurobi.GRB.MAXIMIZE)

# Constraints
r0_x0 = 0.43
r0_x1 = 0.11
r0_x2 = 0.02
upper_bound_r0 = 137

model.addConstr(r0_x0 * milligrams_vitamin_B12 + r0_x1 * milligrams_vitamin_B4 >= 21, name="constraint_B12_B4_min")
model.addConstr(r0_x0 * milligrams_vitamin_B12 + r0_x1 * milligrams_vitamin_B4 <= 104, name="constraint_B12_B4_max")
model.addConstr(r0_x0 * milligrams_vitamin_B12 + r0_x1 * milligrams_vitamin_B4 + r0_x2 * milligrams_vitamin_C <= upper_bound_r0, name="constraint_all")

# Optimize
model.optimize()

# Print solution
if model.status == gurobi.GRB.OPTIMAL:
    print("Optimal Solution:")
    print(f"Milligrams of vitamin B12: {milligrams_vitamin_B12.x}")
    print(f"Milligrams of vitamin B4: {milligrams_vitamin_B4.x}")
    print(f"Milligrams of vitamin C: {milligrams_vitamin_C.x}")
    print(f"Objective: {model.objVal}")
else:
    print("No optimal solution found.")
```