## Problem Description and Formulation

The problem is a linear programming optimization problem. The goal is to minimize the cost of energy drinks R and M while meeting the daily requirements of caffeine and water.

Let's define the decision variables:
- \(R\): the number of cans of energy drink R to buy
- \(M\): the number of cans of energy drink M to buy

The objective function to minimize is the total cost:
\[ \text{Minimize:} \quad 4R + 7M \]

Subject to the constraints:
1. Caffeine requirement: \(2R + 5M \geq 30\)
2. Water requirement: \(5R + 8M \geq 50\)
3. Non-negativity: \(R \geq 0, M \geq 0\)
4. Since we can't buy a fraction of a can, \(R\) and \(M\) should be integers.

## Gurobi Code

To solve this problem using Gurobi in Python, we will use the Gurobi Python interface. First, ensure you have Gurobi installed in your environment. You can install it via pip if you have a Gurobi license:

```bash
pip install gurobi
```

Here's the Gurobi code for the problem:

```python
import gurobi as gp
from gurobi import GRB

# Create a new model
model = gp.Model("energy_drink_problem")

# Define the variables
R = model.addVar(vtype=GRB.INTEGER, name="R")
M = model.addVar(vtype=GRB.INTEGER, name="M")

# Objective function: Minimize 4R + 7M
model.setObjective(4*R + 7*M, GRB.MINIMIZE)

# Constraints
model.addConstr(2*R + 5*M >= 30, name="caffeine_requirement")
model.addConstr(5*R + 8*M >= 50, name="water_requirement")

# Solve the model
model.optimize()

# Check if the model is optimized
if model.status == GRB.OPTIMAL:
    print(f"Optimal solution: R = {R.varValue}, M = {M.varValue}")
    print(f"Minimum cost: ${4*R.varValue + 7*M.varValue}")
else:
    print("The model is infeasible or no solution exists.")
```

This code defines the problem in Gurobi, solves it, and prints out the optimal values for \(R\) and \(M\) if a solution exists. Note that the `vtype=GRB.INTEGER` argument ensures that \(R\) and \(M\) are treated as integer variables, which is crucial for this problem since you cannot buy a fraction of a can of energy drink.