Picking smart numbers like 6 or 100 will give the answer.
Lets say Drum x capacity is 100. Drum Y capacity will be 200.
Oil in drum x is 50
Oil in drum y is 100* 2/3 = 400/3
Fraction of oil in y after x is emptied into y is = (50 + 400/3) / 200
Answer is c
Where did the 6 go? You can't just pick a random number for J because the end result will vary.