Question 64290
X+Y=15 OR X=15-Y
3X=5Y-11 SUBSTITUTING (15-Y) FOR X WE GET
3(15-Y)=5Y-11
45-3Y=5Y-11
-3Y-5Y=-11-45
-8Y=-56
Y=-56/-8
Y=7 SOLUTION 
THEN X=15-7
X=8 SOLUTION
PROOF
3*8=5*7-11
24=35-11
24=24