A psychology professor assigns letter grades on a test according to the following scheme. A: Top 10% of scores B: Scores below the top 10% and above the bottom 55% C: Scores below the top 45% and above the bottom 20% D: Scores below the top 80% and above the bottom 7% F: Bottom 7% of scores Scores on the test are normally distributed with a mean of 67.6 and a standard deviation of 9. Find the numerical limits for a D grade. Round your answers to the nearest whole number, if necessary.