eric has been donating books he no longer needs to his local library. after 3 months of donating, he had 157 books left in his room. after 8 months of donating, he had 102 books left in his room. how many books per month did eric donate on average between monhs 3 and 8?
he donated 18 books per month. you first finds the difference of the books then do use the number of books by the number of months (in this case it was 5 months)
