Correct Answer: $\frac{200}{3}\%$

Solution : Let the cost price of one box as C and the selling price of one box as S.
Given that the selling price of 9 boxes is equal to the cost price of 15 boxes.
⇒ 9S = 15C
⇒ S = $\frac{15}{9}$C = $\frac{5}{3}$C
This means the selling price is $\frac{5}{3}$ times the cost price.
Profit = Selling price – Cost price = $\frac{5}{3}$C – C = $\frac{2}{3}$C
Profit percentage = $\frac{\text{Profit}}{\text{Cost price}}$ × 100
= $\frac{\text{2}}{\text{3}}$ × 100
= $\frac{\text{200}}{\text{3}}\%$
Hence, the correct answer is $\frac{\text{200}}{\text{3}}\%$.