#### Answer

$f(15)=5$

#### Work Step by Step

Substituting $x=15$ in the given function, $
f(x)=\sqrt{x+10}
,$ then
\begin{array}{l}\require{cancel}
f(x)=\sqrt{x+10}
\\\\
f(15)=\sqrt{15+10}
\\\\
f(15)=\sqrt{25}
\\\\
f(15)=\sqrt{(5)^2}
\\\\
f(15)=5
.\end{array}