These are the steps involved..For part b,the seller charged $79.80 (an extra of $19.80 gained) compared to selling 240 apples for $60..The seller can still choose to sell the remaining apples at 25 cents each but that will be an extreme loss..By setting the unit price to 35 cents,the seller makes money..This is why you have to add $19.80 to $60 in illustrating the new price.Hope it helps