1. **State the problem:** A recipe calls for 8 cups of flour and 5 cups of cocoa powder for one batch of brownies. The baker wants to make 3 batches. We need to find how many cups of cocoa powder are needed for 3 batches. 2. **Identify the formula:** The amount of cocoa powder needed scales linearly with the number of batches. So, total cocoa powder needed = (cocoa powder per batch) \times (number of batches). 3. **Apply the formula:** $$\text{Total cocoa powder} = 5 \times 3$$ 4. **Calculate:** $$5 \times 3 = 15$$ 5. **Answer:** The baker should use 15 cups of cocoa powder to make 3 batches of brownies.