Реши уравнения

а) \(9^x-3^{2x-2}=72\) ; \(x=\) [ ];

б) \(\log\_3 x-\log\_9 x+\log\_{81} x=3\) ; \(x=\) [ ];

в) \(\log\_2 (1+\log\_\frac{1}{2} x)=2\) ; \(x=\) [ ].