A sociology professor assigns letter grades on a test according to the following scheme.

A: Top

9%

of scores

B: Scores below the top

9%

and above the bottom

63%

C: Scores below the top

37%

and above the bottom

24%

D: Scores below the top

76%

and above the bottom

7%

F: Bottom

7%

of scores

Scores on the test are normally distributed with a mean of

73.9

and a standard deviation of

9.9

. Find the numerical limits for a D grade. Round your answers to the nearest whole number, if necessary.