Answer
$\frac{6}{7}$
Work Step by Step
According to the textbook, a number, $a$, is a square root of another number, $b$, if $a^2=b$.
$(\frac{6}{7})^2=\frac{36}{49}$, so $\frac{6}{7}$ is a square root of $\frac{36}{49}$.
Therefore: $\sqrt {\frac{36}{49}}=\frac{6}{7}$
