1. **State the problem:** We need to find a formula for the total cost $L$ of a box containing 50 lemons, where each lemon costs $n$ cents. 2. **Formula used:** The total cost is the number of lemons multiplied by the cost per lemon. 3. **Write the formula:** $$L = 50 \times n$$ 4. **Explanation:** Since each lemon costs $n$ cents, and there are 50 lemons, multiplying these gives the total cost in cents. 5. **Final answer:** $$L = 50n$$