# How do you factor 7a^2-ab+28a-4b?

$\left(7 {a}^{2} - a b\right) + \left(28 a - 4 b\right)$ Each bracket has a common factor.
= $a \left(7 a - b\right) + 4 \left(7 a - b\right)$ This creates a common bracket.
= $\left(7 a - b\right) \left(a + 4\right)$