A study indicates that 18- to 24-year olds spend a mean of 135 minutes watching video on their smartphones per month Assume that the amount of time watching video on a smartphone per month is normally distributed and that the standard deviation is 20 minutes. Complete parts (a) through (d) below. a What is the probability that an 18-to 24-year-old spends less than 105 minutes watching video on his or her smartphone per month? The probability that an 18- to 24-year-old spends less than 105 minutes watching video on his or her smartphone per month is (Round to four decimal places as needed.)