Question 115261
X+Y=39 OR X=39-Y
X-Y=7 
NOW REPLACE X BY (39-Y) IN THE SECOND EQUATION & SOLVE FOR Y.
39-Y-Y=7
-2Y=7-39
-2Y=-32
Y=-32/-2
Y=16 ANSWER.
X+16=39
X=39-16
X=23 ANSWER.
PROOF
23-16=7
7=7