As you see, the product of peaches 1 and 2 have the different in cost is $1.35 and $2.70. As well as the following product of peaches also have the same increase in money.
So 2.70 - 1.35 = 1.35 so the common increase would be $1.35
Simply divide your partial amount (18 in this case) by your total (40), and you then multiply your answer from 18/40= .45 by 100, and you get 45. This is 45%