Tom is going to move, he has three kinds of boxes: large, medium, and small. Now he has already 11 large boxes, each of which is either empty or filled with 6 medium boxes. Medium boxes are filled in the large boxes and each of them is either empty or filled with 6 small boxes. Small boxes are empty and filled in the medium boxes. How many boxes does Tom have?
1). he has 56 empty boxes
2). he has 42 small boxes
I pick A
say x filled , then 11 -x empty
=> 6x Medium boxes
say y filled, then 6x-y empty
=> 6y Small boxes
so we need to find, 11 + 6(x+y) ...
now 1 says
(11 -x) + (6x-y) + 6y = 56
=> 5x + 5y = 45
=> x + y = 9
so we can find 11 + 6(x+y) - hence sufficient
nothing about x hence insufficient.