Answer:
71
Step-by-step explanation:
78+31=109 so 180-109=71
4x+2y=18
-2(2x+3y=15)=-4x-6y=-30
-4x-6y=-30
-4y=-12
y=3
2x+3(3)=15
2x+9=15
2x=6
x=3
(3,3)