Each new book donated to a library must be processed. Suppose that the time it takes a librarian to process a book has mean = 10 minutes and standard deviation = 3 minutes. If a librarian has 40 books that must be processed one at a time,
(a) \approx imate the probability that it will take more that 420 minutes to process all these books;
(b) \approx imate the probability that at least 25 books will be processed in the first 240 minutes.