Algebra: A Combined Approach (4th Edition)

$\dfrac{3x-9}{4x-16}=\dfrac{3(x-3)}{4(x-4)}$
$\dfrac{3x-9}{4x-16}$ Take out common factor $3$ in the numerator and common factor $4$ in the denominator: $\dfrac{3x-9}{4x-16}=\dfrac{3(x-3)}{4(x-4)}$