A local club is selling Christmas trees and deciding how many to stock for the month of December. If demand is normally distributed with a mean of 100 and standard deviation of 20, trees have no salvage value at the end of the month, trees cost $20, and trees sell for $50 what is the service level?
a) .20
b) .60
c) .40
d) .84
e) unable to determine given the above information.