The wrong numbers are added and subtracted. It should be:
The men pay 30
The waiter gives 3 back, so the men paid 27 and the waiter got 27
The food was 25, so the waiter can keep 2 dollars.
The wrong numbers are added and subtracted. It should be:
The men pay 30
The waiter gives 3 back, so the men paid 27 and the waiter got 27
The food was 25, so the waiter can keep 2 dollars.