Since the KE = the PE at the requested height
2PE = total available energy = 20W where W is the weight of the object, presumably in pounds. Too bad this isn't in SI units.
Thus the PE is 10W at the requested height, but this is also Wh
Wh = 10W so h = 10 feet.
In the second part of your question all of the available potential energy is converted to KE so
20W = (0.5*WV^2) / 32 since the acceleration due to gravity in the English system is 32 ft / s^2.
W cancels out and V = 3.5.8 ft / s