Question

How do you solve the system `7x - 8y = 112` and `y = -2x +9` by substitution?

Answer 1

You substitute the `y`-value of the second equation into the first:

`->7x-8*(-2x+9)=112`
`->7x+16x-72=112`
`->23x=184->x=184/23=8`

Now put back the value of `x` in the second equation:
`y=-2*8+9=-7`

So `x=8 and y=-7`

Check your answer with the first equation:
`7*8-8*(-7)=56-(-56)=112` check!