Answer:
Rs.3
Explanation:
According to the scenario, computation of the given data are as follows,
Price of 12 boxes = Rs. 900
So, price of 1 box = Rs. 900 ÷ 12 = Rs. 75
Selling price for 5 boxes = Rs. 390
So, Selling price of 1 box = Rs. 390 ÷ 5 = Rs. 78
So, Profit or Loss = Selling price - Purchase price
= Rs. 78 - Rs.75
Profit = Rs.3 ( positive means profit)
Hence, his gain on one box is Rs.3.