# How do you combine (ab - 9) - (6ab + 8) ?

$\left(a b - 9\right) - \left(6 a b + 8\right) = a b - 9 - 6 a b - 8$
$= \left(a b - 6 a b\right) - \left(9 + 8\right)$
 = color(green)(-5ab - 17