(1 point) A mailorder house uses an average of 350 mailing bags each day. The number of bags needed each day is approximately normally distributed, with a = 50. (a) On Tuesday, what is the probability they use 420 or fewer bags? (Hound your answer to four decimal places.) (b) If they want to be 83% certain that all orders can be filled, how many bags should they have at the beginning of each day? (Hint: Since this is a number of bags, it must be a whole number.)