A Nielsen study indicates that 18- to 34-year olds spend a mean of 116 minutes watching video on their smartphones per week during the fourth quarter of 2016. Assume that the amount of time watching video on a smartphone per week is normally distributed and that the standard deviation is 15 minutes.

a. What is the probability that an 18- to 34-year-old spends less than 97 minutes watching video on his or her smartphone per week?

b. What is the probability that an 18- to 34-year-old spends between 97 minutes and 129 minutes watching video on his or her smartphone per week?

c. What is the probability that an 18- to 34-year-old spends more than 129 minutes watching video on his or her smartphone per week?

d. One percent of all 18- to 34-year-olds will spend less than how many minutes watching video on his or her smartphone per week?