Answer
$3\sqrt{2} \text{ cm}$
Work Step by Step
Using $a^2+b^2=c^2$ (or the Pythagorean Theorem) with legs having measures $3$ and $3$, then the hypotenuse, $c$, is
\begin{array}{l}\require{cancel}
3^2+3^2=c^2
\\\\
9+9=c^2
\\\\
18=c^2
\\\\
c=\sqrt{18}
\\\\
c=\sqrt{9\cdot2}
\\\\
c=\sqrt{(3)^2\cdot2}
\\\\
c=3\sqrt{2}
.\end{array}
Hence the hypotenuse is $
3\sqrt{2} \text{ cm}
.$
