$ 3^{3x-1}=36 \Rightarrow 3^{3x-2}=3^{(3x-1)-1} = \frac{3^{3x-1}}{3^1} = \frac{36}{3}=12 \\  \sqrt{\sqrt{3^{3x-2}+13}+139} = \sqrt{\sqrt{12+13}+139} = \sqrt{\sqrt{25}+139} = \sqrt{5+139} = \sqrt{144}=12 $