Physics - need help solving (b)

(a ) What is the final velocity, in m/s, of a hoop that rolls without slipping down a 5.50 m high hill, starting from rest? 7.345 m/s (b) What would be the final velocity, in m/s, if a disk of the same mass and radius as the hoop rolled down the hill? 0.482 X What is the moment of inertia of a solid disk? m/s