4*55-43-57-62=58

2x+20+3x+4X-20= 180，x=20。

Foreigners are used to this question and don't understand that you and your friend are the same person, so you spent 3 yuan, and the actual cost was 3.6 yuan. That 0.6 is a tip, 0.6/3=20%, and so is a friend's. The key is that you can't understand the meaning of this question, aa, or are you alone? Why don't you turn it over?