Help me check and explain please!

A newspaper boy is trying to perfect his business in order to maximize the money he can save for a new car. Daily paper sales are normally distributed, with a mean of 100 and standard deviation of 10 . He sells papers for $0.50 and pays $0.30 for them. Unsold papers are trashed with no salvage value. Please show steps. a) How many papers should he order each day? ( 6pts ) b) What's the probability that there will he experience a stock-out? (4 pts)