Answer
$c=17 \text{ } m$
Work Step by Step
Using $a^2+b^2=c^2$ or the Pythagorean Theorem, then,
\begin{array}{l}\require{cancel}
8^2+15^2=c^2
\\\\
64+225=c^2
\\\\
289=c^2
\\\\
c=\pm\sqrt{289}
\\\\
c=\pm\sqrt{(17)^2}
\\\\
c=\pm17
.\end{array}
Since there are no negative measurements, then $
c=17 \text{ } m
.$