Suppose the hourly dollar amount of food sold by a local restaurant follows an approximately mound-shaped distribution, with a mean sales level of $400 per hour and a standard deviation of $60 per hour.

a. During what percentage of working hours does this restaurant sell between $280 and $520 worth of food per hour? Explain.

b. During a one-hour period, this restaurant had sales at the 84th percentile. What dollar sales figure does this represent?