Average sales for an online textbook distributor were $67.63 per customer per purchase. Assume the sales are normally distributed. If the standard deviation of the amount spent on textbooks is $8.96, find these probabilities for a randomly selected customer of the online textbook distributor. Round your answer to the nearest tenth of a percent. (a)He or she spent more than $85.55 per purchase. (b)He or she spent less than $76.59 per purchase