TeX джерело:

\begin{array}{l}{3^x} - 2 \cdot {3^{x - 2}} = 63;\;{3^{x - 2}}({3^2} - 2) = 63;\;{3^{x - 2}} \cdot 7 = 63;\;{3^{x - 2}} = 9;\;x - 2 = 2;\\x = 4.\end{array}