TeX source:

\begin{aligned} log \left(\frac{2x^2+6x}{3x+9}\right) &= log \left(\frac{2x(x+3)}{3(x+3)} \right) & & \text { Factor the numerator and denominator. } \\ &=log \left( \frac{2x}{3} \right) & & \text { Cancel the common factors. } \end{aligned}