#### Answer

$\dfrac{7a}{\sqrt{42ab}}$

#### Work Step by Step

Rationalizing the numerator, the given expression, $
\sqrt{\dfrac{7a}{6b}}
,$ is equivalent to
\begin{array}{l}
\sqrt{\dfrac{7a}{6b}\cdot\dfrac{7a}{7a}}
\\\\=
\sqrt{\dfrac{(7a)^2}{42ab}}
\\\\=
\dfrac{7a}{\sqrt{42ab}}
.\end{array}