The frequency of A's would be 16.
The following would be the relative frequencies after the initial .08.
.18, .45, .15, .14.
To find the frequency of A, start by subtracting all of the other values from the total number. There are 200 total students, so subtract the other grade ranges.
200 - 36 - 90 - 30 - 28 = 16.
Now to find all of the frequencies, just divide each value by the total (200).
36/200 - .18
90/200 = .45
30/200 = .15
28/200 = .14