Each problem gives a price and the amount handed over, and the student works out the change. The amount paid is always something a person would actually use - the next dollar up, or a round five or ten - so the problems read like real purchases.
The answer key gives the change as an amount. Counting up from the price is the method most people use, and a student can do it here even though the worksheet does not walk through the steps.
Start at the price and count up to the amount paid: coins to the next ten cents, then to the next dollar, then dollars. The total you counted is the change.
Because that is what happens at a till. You do not pay $7.43 for a $6.18 item - you hand over a ten, or seven ones, or a five and three ones.
The answer is the same as a subtraction, but counting up is easier to do in your head and is how it is actually done. The subtracting money page is the column-arithmetic version.
Prices under $10 by default. Set Amounts to Under $100 for larger purchases and larger notes.