In a large section of a history class, the points for the final exam are normally distributed with a mean of 72 and a standard deviation of 9. Grades are assigned according to the rule below.

• the top 10% receive an A
• the next 20% receive a B
• the middle 40% receive a C
• The next 20% receive a D
• the bottom 10% receive an F

find the lowest score on the final exam that would qualify a student for

(a) an A

(b) a B

(c) a C

(d) a D