Question

Consider the system of equations.

Answer 1

We know that
The subtraction property of equality tells us that if we subtract from one side of an equation, we also must subtract from the other side of the equation to keep the equation the same

that means

if a=b  and  c=d
a-c=b-d

then 
−8x+4y=0----------> equation 1
a=(-8x+4y)    b=0

−8x+7y=6----------> equation 2
c=(-8x+7y)   d=6

therefore

(-8x+4y)-(-8x+7y)=0-6
-8x+4y+8x-7y=-6
-3y=-6

the answer is the option 
Subtraction Property of Equality