Question

What are `x` and `y` if `-x-3y= 15` and `2x+7y= -36`?

Answer 1

`3` for `x` and `-6` for `y`

Explanation:

Let's solve for `x`:

`-x-3y = 15`

`-x = 15+3y`

`x = -15-3y`

`* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *`

Now let's substitute that into the second equation

`2(-15-3y) + 7y = -36`

`-30 - 6y + 7y = -36`

`-6y + 7y = -6`

`y = -6`

`* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *`

Now we need to solve for `x`:

`x = -15-3(-6)`

`x = -15 + 18`

`x = 3`

`* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *`

We should still check our work:
Plug in `3` for `x` and `-6` for `y`

`-(3) - 3(-6)` should equal `15`

`-3 - (-18)`

`-3+18 = 15`

`15 = 15`, so we were right!!!