Why solving systems of equations by substitution, you substitute the expression for one variable for that variable in the other equation.
8.
y = -1/4x
x + 2y = 4
Substitute -1/4x for y in x + 2y = 4 and solve:
x + 2(-1/4x) = 4
x - 1/2x = 4
x/2 = 4
x = 8
Now that you have x, you can substitute it into one of the original equations to find y:
x + 2y = 4
8 + 2y = 4
2y = -4
y = -2
The last step is to check your work by substituting back into both original equations:
y = -1/4x
-2 = -1/4(8)
-2 = -2
x + 2y = 4
8 + 2(-2) = 4
8 - 4 = 4
4 = 4
Answer:
x = 8
y = -2