#### Answer

$5$

#### Work Step by Step

RECALL:
The distance between the points $(x_1, y_1)$ and $(x_2, y_2)$ can be found using the distance formula
$d=\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}$
Use the formula above to obtain:
$d=\sqrt{(8-5)^2+(5-1)^2}
\\d=\sqrt{3^2+4^2}
\\d=\sqrt{9+16}
\\d=\sqrt{25}
\\d=\sqrt{5^2}
\\d=5$