What is 13^3x-1=91 solved?

The answer is 0.041875294788348

13^(3x-1) = 91

(3x - 1)ln 13 = ln 91 

(3x - 1)ln 13 = ln 13 + ln 7

(3x - 2)ln 13 = ln 7

$3x - 2 = \dfrac{\ln 7}{\ln13}=\log_{13}7$

$x = \dfrac{\log_{13}7+2}{3}$

And then use ur calculator to get 0.919551471