Step-by-step explanation:
[tex]y = 5x \\ y = 9x + 4 \\substitute \:y = 5x \: to \: the \: other \: equation \\ y = 9x + 4 \\5x = 9x + 4 \\ 5x - 9x = 4 \\ - 4x = 4 \\ x = \frac{4}{ - 4} \\ x = - 1[/tex]
