How many apps? According to a website, the mean number of apps on a smartphone in the United States is 80. Assume the number of apps is normally distributed with a mean of 80 and a standard deviation of 28.

(a) What proportion of phones have between 66 and 91 apps? Round the answer to four decimal places.
(b) Find the 90th percentile of the number of apps. Round the answer to two decimal places.