How do you combine  (-18x^2 + 4x - 16) - (15x^2 + 4x - 13)?

$- 18 {x}^{2} + 4 x - 16 - 15 {x}^{2} - 4 x + 13$
=color(blue)(-18x^2 - 15x^2 + color(blue)(4x - 4x) - color(blue)(16 +13
$= \textcolor{b l u e}{- 33 {x}^{2} + 0 - \textcolor{b l u e}{3}}$
$= - 33 {x}^{2} - 3$