help me check! 2 parts 1 question

Unbeknownst to each other, both Harry and Garry decide to institute a retail-level rebate on a specific high-end stove. The prices of the stove are $1,000 and $900 in Harry's and Garry's store, respectively. Both Harry and Garry's rebate offers will be advertised in the Sunday paper and will last one week. Neither Harry nor Garry has done the research necessary to discover the Just Noticeable Difference (which, for the target market and that product category in that economic climate, is 20% ). Both Harry and Garry decided to offer consumers a $180 rebate on their stoves. Harry sold 35 stoves during the rebate period, which is about the same number that he sold the week just prior to the rebate offer. Garry sold 40 stoves during the rebate period, which is an increase of about 10 more than he sold the week just prior to the rebate offer. Did the fact that he did not know the accurate Just Noticeable Difference cost Harry any Money ( 3 points)? Yes/No (Circle one). If yes, how much? (Please specify how you get your answer, otherwise no credit will be given.) Did the fact that he did not know the accurate Just Noticeable Difference cost Garry any Money ( 3 points)? Yes/No (Circle one). If yes, how much? (Please specify how you get your answer, otherwise no credit will be given.)