Answer:
C) he prefers (6, 6) over both (3, 9) and (9, 3).
Explanation:
Robert has 3 options for combinations of X and Y that is (3, 9), (6, 6), and (9, 3).
If he is indifferent to combinations (3,9) and (9,3). It means his preference is the third option (6,6).
Robert prefers to have equal combination of X and Y.