# How do you combine (-16x^2 + 13x - 13) - (-19x^2 - 11x + 12)?

Because of the $-$sign you reverse all the signs in the second term (and of course you change the $-$ into a $+$:
$= \left(- 16 {x}^{2} + 13 x - 13\right) + \left(19 {x}^{2} + 11 x - 12\right)$
$= - 16 {x}^{2} + 13 x - 13 + 19 {x}^{2} + 11 x - 12$
$= \left(- 16 {x}^{2} + 19 {x}^{2}\right) + \left(13 x + 11 x\right) + \left(- 13 - 12\right)$
$= 3 {x}^{2} + 24 x - 25$