# How do you solve the system using the substitution method for x+y=9 and y=12?

Sep 11, 2015

Substitute $12$ for $y$ in $x + y = 9$
to get $x = - 3$

#### Explanation:

Given
[1]$\textcolor{w h i t e}{\text{XXX}} x + y = 9$
[2]$\textcolor{w h i t e}{\text{XXX}} y = 12$

Based on [2] we can substitute $12$ for $y$ in [1]
[3]$\textcolor{w h i t e}{\text{XXX}} x + 12 = 9$

Subtracting $12$ from both sides gives
[5]$\textcolor{w h i t e}{\text{XXX}} x = - 3$