Express Courier Service has found that the delivery time for packages is normally distributed, with mean 14 hours and standard deviation 2 hours.
(a) For a package selected at random, what is the probability that it will be delivered in 18 hours or less?
(b) What should be the guaranteed delivery time on all packages in order to be 95% sure that the package will be delivered before this time? That 5% of the packages will be delivered at a time beyond the guaranteed time period.