Prime numbers are those numbers, which don't have factors other than 0 and itself.

Prime numbers are 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61 67, 73, 79 between 16-80

The count of above list is 15

Prime numbers between 90 to 100 are 97

The count is 1

Sum of counts = 15+1 = 16