# How do you solve this system of equations using the substitution method x- y = 4 and 6x + 4y = - 66?

Oct 19, 2017

$y = - 9 , x = - 5$

#### Explanation:

$x - y = 4 \Rightarrow$ equation 1
$6 x + 4 y = - 66 \Rightarrow$ equation 2

Make either $x$ or $y$ the subject of equation 1, so you can substitute the values of in into equation 2.

$x = 4 + y$

Substitute this into equation 2.

$6 \left(4 + y\right) + 4 y = - 66$
$24 + 6 y + 4 y = - 66$
$10 y = - 90$
$\therefore y = - 9$

To find $x$, substitute $y = - 9$ back into either equation 1 or 2.

$x - \left(- 9\right) = 4$
$x = 4 - 9$
$\therefore x = - 5$