There are a lot of definitions of change and it depends on how it is used. Yours did not specify to what kind of change this would be. But you are given 40 and then it is increased by 12.5. Add the two values you get 52.5. This would be your answer if you were asked to find the final amount of the increased number. However, you were asked to the amount of CHANGE in this problem. So, the amount of change is 12.5.