Answer
$\dfrac{13\sqrt{10}}{20}$
Work Step by Step
Rationalize the denominator by multiplying $\sqrt{10}$ to both the numerator and denominator:
$=\dfrac{13\sqrt{10}}{\sqrt{40}(\sqrt{10})}
\\=\dfrac{13\sqrt{10}}{\sqrt{400}}
\\=\dfrac{13\sqrt{10}}{20}$