Answer
$$5\sqrt3$$
Work Step by Step
RECALL:
(1) For any real numbers $a \ge 0, b\ge0$, $\sqrt{ab}=\sqrt{a} \cdot \sqrt{b}$
(2) For any real numbers $a \ge 0, b\gt 0$, $\sqrt{\dfrac{a}{b}}=\dfrac{\sqrt{a}}{\sqrt{b}}$
Note that $75=25(3)$.
Thus, using rule (1) above gives:
\begin{align*}
\sqrt{75}&=\sqrt{25(3)}\\
&=\sqrt{25} \cdot \sqrt3\\
&=5\sqrt3
\end{align*}