3 In a certain town, the time, \(X\) hours, for which people watch television in a week has a normal distribution with mean 15.8 hours and standard deviation 4.2 hours.
- Find the probability that a randomly chosen person from this town watches television for less than 21 hours in a week.
- Find the value of \(k\) such that \(\mathrm { P } ( X < k ) = 0.75\).