What is the spring Constant of a spring that needs a force of 6 N to be compressed from 0.40m to 0.35 m

What is the spring constant of a spring that stores 25 J of elasticpotential energy when compressed by 7.0 cm from its relaxedlength?
_____ N/m

What is the spring constant of a spring that stores 25 J of elastic potential energy when compressed to 7.5 cm

A mass and spring are arranged on a horizontal, frictionless table. The spring constant is k=500 N/m, and the mass is 4.5 kg. The block is pushed against the spring so that the spring is compressed an amount 0.35 meters and then released. Find the velocity of the mass when it leaves the spring?