A Nielsen study indicates that 18- to 24- year olds spend a mean of 174 minutes watching video on their smartphones per month. Assume that the amount of time watching a video on a smartphone per month is normally distributed and that the standard deviation is 15 minutes.

a. What is the probability that an 18- to 24-year-old spends less than 150 minutes watching video on his or her smartphone per month?

b. What is the probability that an 18- to 24-year-old spends between 150 and 198 minutes watching video on his or her smartphone per month?

c. What is the probability that an 18- to 24-year-old spends more than 198 minutes watching video on his or her smartphone per month?

d. One percent of all 18- to 24-year-olds will spend less than how many minutes watching video on his or her smartphone per month?