Answer:
x=9, y=3
Step-by-step explanation:
-4x+6y=-18
y=-2x+21
-4x+6(-2x+21)=-18
-4x-12x+126=-18
144=16x
x=9
y=-18+21
y=3
Answer: this is a function.
f(x)=y
domain -> 1,2,3
values: 3,7,-1