Respuesta :

X-Y=4

X=Y+4

(Y+4)+Y=20

2Y=20-4

Y=16/2

Y=8 ANSWER.

Explanation:

 X-8=4

X=4+8

X=12 ANSWER.

PROOFS:

8+12=20

20=20

8-4=4

4=4

X=12 that the answer