I believe the answer is b. There are several ways to find the answer. what I did was I just counted it out in my head AKA the long way..
(1) 2/3 then
(2) 4/3 which is 1 and 1 /3
(3) 6/3 which is 2 cups
(4) 8/3 which is 2 and 2/3
(5) 10/3 which is 3 and 1/3
(6) 12/3 which is 4
(7) 14/3 which is 4 and 1/3
(8) 16/3 which is 5 and 2/3
(9) 18/3 which is 6
another way to do it would be 6x3=18.. 18/2=9 i just like to double check myself