Rachel is making T-shirts that she hopes to sell at the upcoming “War on War” concert. The T-shirts cost $6 each to produce, and she will price them at $20 each. She expects that she can donate any unsold T-shirts to a local charity for a tax write-off of $2 each. Based on her experience at past concerts, Rachel expects to sell 1,000 T-shirts, with a standard deviation of 100 T-shirts.

a. How many T-shirts should Rachel make?
b. What is the probability that she will run out of shirts to sell?