Given the following about a spring:

mass = 20.0 kg
height initial = 5.25 m (above the ground)
height final = 2.17 m (above the ground with the mass attached)
delta y initial = 0.00 m

There are several questions I must answer from this.

1. What is the value of the spring constant?

I have solved this with the formula kx = mg, which gave me the value of 63.7 N/m as k.

2. What would the velocity of the falling mass be half way down?

3. How much work would it take to return the mass to its original position?

I really am not sure how to go about two and three. All help is appreciated!!!