Thank you for your reply. I am afraid that you misunderstood my question. 1 unit of X may be larger than 1 unit of Y. Hence, we can’t conclude that the shaded part of Z is 2 units.
Lets say X = 60 cm2 , Y = 45 cm2 , Z = 60 cm2
In this situation, the shaded part of X is 10 cm2 (1/6 x 60 =10) the total shaded of Y is 27 cm2 (3/5 x 45), then the remaining shaded part of Z is 17 cm2 (27 – 10). As a result, the ratio will not work.
I tried solving this question and got stuck because of this problem. In order for a particular math concept to apply, it must work in all situations.