Substituting equations to solve.

Example Question:
x= y-7
-y=2x=8


Example to solve substituting equations to solve..

substitute 1st equation into the 2nd one

-y = 2*(y-7) - 8
-y = 2y - 14 - 8
-y = 2y - 22
-y - 2y = -22
-3y = -22
y= 22/3

substitute the value of y in the 1st equation to get x.