A research marketer for an online retail store was interested in the number of times per month stay-at-home moms bought items from online retail stores. She found the mean is 15 items and the standard deviation is 3 items purchased from online retail stores each month. Using the empirical rule, approximately what percent of stay-at-home moms bought more than 21 items from online retail stores each month?

2.50%
5.0%
10.0%
16.0%
95.0%