# How do you solve 72x - 8y = 40 and y = 9x + 5 using substitution?

Jul 9, 2016

This pair of equations is inconsistent; there are no solutions.

#### Explanation:

To see that there are no solutions:

Given
[1]$\textcolor{w h i t e}{\text{XXX}} 72 x - 8 y = 40$
[2]$\textcolor{w h i t e}{\text{XXX}} y = 9 x + 5$
substituting $\left(9 x + 5\right)$ (from [2]) for $y$ in [1]
[3]$\textcolor{w h i t e}{\text{XXX}} 72 x - 8 \left(9 x + 5\right) = 40$
[4]$\textcolor{w h i t e}{\text{XXX}} - 40 = 40$ (which is clearly impossible)