C2 Exponential Graph and Log question

I am really stuck on 5c and i have got the mark scheme but I dont understand it . any help would be appreciated

Which bit don't you undertstand?

We can write $\left(\frac{1}{3} \right)^x = \frac{1}{3^x}$, so if we equate the two equations we have $\frac{1}{3^x} = 2 3^x$

Multiply both sides by the denominator of the LHS:

$1 = 3^x \times 2 \times 3^x$ but you know what the same thing multiplied by itself is, don't you? It's a square. So:

$1 = 2 \times (3^x)^2$. Now divide both sides by 2:

$\frac{1}{2} = (3^x)^2$. Now take the square root:

$\pm \sqrt{\frac{1}{2}} = 3^x$. reject the negative value because exponentials are always positive.

SO $3^x = \sqrt{1/2}$. Take logarithms to solve: $x \ln 3 = \ln \sqrt{1/2}$. Isolate $x$.

hey thanks i just forgot
. thank you !