[tex]Domain:x > 0\\\\2\log_7x=\log_727+\log_73\\\\\text{use}\ \log x^n=n\log x\ \text{and}\ \log x+\log y=\log(xy)\\\\\log_7x^2=\log_7(27\cdot3)\iff x^2=81\to x=\sqrt{81}\to\boxed{x=9}[/tex]
