How do you simplify (sqrt5)^6?

You need this property: ${\left({x}^{a}\right)}^{b} = {x}^{a b}$,
and this equallity: $\sqrt{x} = {x}^{\frac{1}{2}}$,
to simplify: ${\left(\sqrt{5}\right)}^{6} = {\left({5}^{\frac{1}{2}}\right)}^{6} = {5}^{\frac{6}{2}} = {5}^{3} = 125$