[tex]9 ^{x} \times 3 {}^{x - 1} = 9 {}^{4} [/tex]
[tex](3 {}^{2} ) {}^{x} \times 3 {}^{x - 1} = (3 {}^{2} ) {}^{4} [/tex]
[tex]3 {}^{2x} \times 3 {}^{x - 1} = 3 {}^{8} [/tex]
[tex]2x + x - 1 = 8[/tex]
[tex]2x + x = 8 + 1[/tex]
[tex]3x = 9[/tex]
[tex]x = 3[/tex]
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