A study by the National Golf Foundation reports that the 6.2 million golfers over the age of 50 spent an average of $939 on golf during the previous year. Assuming a normal distribution with a standard deviation of $200, what is the probability that a randomly selected golfer in this age group will have spent:
a. more than $1539?
b. between $939 and $1339?
c. less than $1139?
d. between $539 and $1139?