(if it's frictionless the length doesn't even matter :) )
It would have the same kinetic energy down as the potential energy up. That is, \(mgh=\frac{mv^2}{2}\) or \(2gh=v^2\) (the mass doesn't even matter). The result is \(\sqrt{2gh}\), so only the height matters really. It is almost 9 (it is \(\sqrt{80}=4\sqrt{5}\)).