Grateful Fred sells souvenir T-shirts at rock concerts. The shirts arc specially ordered with the city and date of the concert, so he cannot take them to another city after the concert. He buys the shirts for S15 each and sells them for $35 before and during the concert. He sells any remaining shirts outside the concert grounds for $10 after the concert ends, and can usually dispose of all of them. For typical concert, demand is normally distributed, with a mean of 2, 500 and standard deviation of 200. How many shirts should Fred order?