A recent study of the hourly wages of maintenance crews for major airlines showed that the mean hourly salary was $16.50, with a standard deviation of $3.50. If we select a crew member at random, what is the probability the crew member earns:
a. Between $16.50 and $20.00 per hour?
b. More than $20.00 per hour?
c. Less than $15.00 per hour?