Answer
$d\approx21.541
\text{ units}
$
Work Step by Step
Using $d=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}$ or the Distance Formula, the distance, $d$, between the given points, $(
5,21
) \text{ and } (
-3,1
),$ is
\begin{array}{l}\require{cancel}
d=\sqrt{(5-(-3))^2+(21-1)^2}
\\\\
d=\sqrt{(8)^2+(20)^2}
\\\\
d=\sqrt{64+400}
\\\\
d=\sqrt{464}
\\\\
d\approx21.541
\text{ units}
.\end{array}