Answer:
The answer is D(20)
Explanation:
I don't know the exact algebraic explanation, however, this is how I did it.

If you divide the second equation into seperate twos, you will get 2*2*2*2*2*2 =

Therefore,
meaning that x is equal to 6. Now The next bit is trial and error, 20-6=14.

Last thing to do is to add x+y=6+14. That is why the answer is 20.
If you wait a bit longer, someone will probably have a more algebraic explanation, however, you stated you only needed the answer so I hope this helped.