#### Answer

$6x$

#### Work Step by Step

Using the rule given in the book:
If $n$ is an even positive integer, then $\sqrt[n]{a^n} = |a|$
If $n$ is an odd positive integer, then $\sqrt[n]{a^n} = a$
We get $\sqrt{36x^2} = \sqrt{(6x)^2} \rightarrow |6x| = 6x$