An apple vendor bought 60 boxes of apples. He sold 40 boxes in the morning, each at a price 30% more than what he paid for. In a rush to sell all the boxes by the end of the day, he then sold the remaining boxes in the afternoon, each at a price 20% less than what he paid for. His profit, after paying the stall rental fee of 800 pesos , was 6800 pesos. How much is one box of apples?