Question

How do you solve the system of equations `x- 7y = 21` and `2x - 7y = 28`?

Answer 1

`x = 7` and `y = -2`

Explanation:

`x-7y = 21`
`2x - 7y = 28`

Subtracting the second equation from the first equation:
`2x - 7y - (x - 7y) = 28-21`
`2x - 7y -x + 7y = 7`
`x = 7`

Plugging in `7` for `x` in the first equation:
`7-7y = 21`
`7 = 21 + 7y`
`7y = 7-21`
`7y = -14`
`y = -14/7`
`y = -2`