An English Puzzle:Please give your answer and explanations in English.

题目

An English Puzzle:Please give your answer and explanations in English.
A farmer buys a horse for $60.He sells it to his neighbor for $70.Then he discovers he could have made more money if he had sold it at a higher price.He borrows $10 from his wife,and buys the horse back for $80.He then sells it to another neighbor for $90.How much money did he make?Of course the money he made doesn’t include the ten dollars borrowed form his wife.
The question:How much money did he make?

答案

The farmer's total cost: 60 + 70 = 130
His total income: 70 + 90 = 160
His profit: 160 - 130 = 30
Deduct $10 he borrowed from his wife: 30 -10 = 20
Answer: He made $20.