You probably rewrote the equation as $\displaystyle{{9}}^{{{6}}}={{3}}^{{{4}{x}-{4}}}\usepackage{cmbright}\Huge\$ , which is true, but then incorrectly set the exponents equal to each other and solved for x. Those exponents are not equal because the bases are not equal. Instead, rewrite the equation as $\displaystyle{{9}}^{{{6}}}={{9}}^{{{2}{x}-{2}}}\usepackage{cmbright}\Huge\$ , and then set the exponents equal.