Five coppers is a meal for one person and three people, so the meal for three people should be 15 coppers. This meal used 500 grams of rice, so the price of 100 grams of rice should be 3 copper coins. A gave 200 grams of rice, which is 6 copper coins according to the money. He had dinner together, so he only got 1 copper coins. B gave 300 grams of rice, which is 9 copper coins according to the money. He also ate together, so he should deduct five coppers, so he should take four coppers. (in the collection of primary school knowledge)