Door spring problem, physics homework help

A door spring is difficult to stretch.

a.

What maximum force do you need to exert on a relaxed spring with a 1.2×10⁴-N/m spring constant to stretch it 6.0 cm from its equilibrium position?

b.How much does the elastic potential energy of the spring change?

c. Determine its change in elastic potential energy as it returns from the 6.0-cm stretch position to a 3.0-cm stretch position.

d. Determine its elastic potential energy change as it moves from the 3.0-cm stretch position back to its equilibrium position.