An English professor assigns letter grades on a test according to the following scheme.

A: Top 13%

of scores

B: Scores below the top 13%

and above the bottom 61%

C: Scores below the top 39%

and above the bottom 22%

D: Scores below the top 78%

and above the bottom 6%

F: Bottom 6%

of scores

Scores on the test are normally distributed with a mean of 75.1

and a standard deviation of 9.1. Find the numerical limits for a D grade. Round your answers to the nearest whole number, if necessary.