well, let's notice something, we have two 45° angles, now each of those will give use an equal opposite side, namely if that one side is "x", the other is her twin, "x" as well.
is a right-triangle, so we can use the pythagorean theorem, and we know the sides are x,x,6.
[tex]\bf \textit{using the pythagorean theorem} \\\\ c^2=a^2+b^2\implies 6^2=x^2+x^2 \qquad \begin{cases} c=\stackrel{hypotenuse}{6}\\ a=\stackrel{adjacent}{x}\\ b=\stackrel{opposite}{x}\\ \end{cases} \\\\\\ 36=2x^2\implies \cfrac{36}{2}=x^2\implies 18=x^2\implies \sqrt{18}=x\implies \sqrt{9\cdot 2}=x \\\\\\ \sqrt{3^2\cdot 2}=x\implies \boxed{3\sqrt{2}=x}[/tex]
