in the united states the ages 13 to 55+ of smart phone users approximately follow a normal distribution with approximate mean and standard deviation of 36.9 years and 13.9 year's respectively

A. determine the probability that a random smartphone user in the age range 13 to 55+ is between 23 and 64.7 years old

B. determine the probability that a randomly selected smart phone user is at most 50.8

C. find the 80th percentile of this distribution, and interpret in a complete sentence