2. $\begin{array}{rcl}{\color{blue}\log (}7^{x+10}{\color{blue})} & = & {\color{blue}\log (}15^{10x}{\color{blue})} \\ (x+10) \cdot \log 7 & = & 10x \cdot \log 15 \quad (\text{Property of logs: } \log a^b = b\log a) \\ (\log 7)x + 10\log 7 & = & (10\log15)x \\ & \vdots & \end{array}$