Part A:
Jason has 3 1/2 bars and he give 3/4 to as many of his friends as possible. So you divide 3 1/2 by 3/4 and you get 4 2/3. You choose 4 because there are not enough left for another person.
Part B:
If you did your math correctly and got 4 2/3 you subtract 4. So Jason has 2/3 left for himself.