Here's how I solved:
Object B = 100 - 80 (4th diagram minus 3rd diagram)
(so option A is correct)
Object C = 75 - 40 - 20 (2nd diagram minus 1st diagram - Object b)
(so option B is correct)
Just to be sure, I checked option D (most straightforward): Objects A B and C = 100 - 40. Hence, option D is incorrect.
haha.. so answer should be 2.