salloni... u missed the biggest part of the question.... how many credits they took in each semesters?? Full time student = 12 or over for Undergrad and 9 or over for Grad... so they might have taken different credit hours. In that case, it is possible.

Calculation Hint:

if credit hours "3" = 3* 4 = 12 (its like out of or full marks for 3 credit hour class)

A = 12

B = 9

C = 3

F = 0

I think you can calculate on your own now.