# How do you solve 4x + 5y = 18 and x = 39 -7y using substitution?

Apr 21, 2016

$y = 6$
$x = - 3$

#### Explanation:

$4 x + 5 y = 18$ -----1
$x = 39 - 7 y$-----2

subtitute equation 2 into equation 1

$4 \left(39 - 7 y\right) + 5 y = 18$
$156 - 28 y + 5 y = 18$
$156 - 23 y = 18$
$- 23 y = - 138$
$y = 6$

subtitute $y = 6$ into equation 2

$x = 39 - 7 \left(6\right)$
$x = - 3$