## Precalculus (6th Edition)

$-3$
Given that we know $y=0$ is part of the solution set, we back-substitute it into one of the initial equations: $6x+y=-18$ $6x+0=-18$ $6x=-18\quad/\div 6$ $x=-3$ Confirm by substituting into the second equation, $13(-3)+(0)=-39.$