The scores on an examination are normally distributed with mean p = 70 and standard deviation a

Question:

The scores on an examination are normally distributed with mean p = 70 and standard deviation a = 8. Suppose that the instructor decides to assign letter grades according to the following scheme (left endpoint included).
Scores Grade
Less than 58...................... F
58 to 66........................... D
66 to 74........................... C
74 to 82........................... B
82 and above..................... A
Find the percentage of students in each grade category.