# How do you combine (5a + 9b) - (2a + 4b)?

Regroup with the terms that include the variable $a$ in one group and the terms that include the variable $b$ in the other.
$\left(5 a + 9 b\right) - \left(2 a + 4 b\right)$
$= \left(5 a - 2 a\right) + \left(9 b - 4 b\right)$
$= 3 a + 5 b$