You can calculate it: shopping (expenditure) 18.

O to W 108 (revenue)

W stands for O 90 (change)

10+90= 108 account is fine.

In addition, you should pay attention to "now W has 103 yuan in his hand and gave it to O 90 yuan, 103-90 = 13". Now W has 103, giving 90. O After paying back the money, W already has 103+90= 193.

O Before paying back the money, W should have money 193- 108=85 (twenty yuan, three tens, two fives).

You have neglected that W already has money in his hand 85+ 18= 103.