Compressed spring on the ceiling.

[mistabry]

Homework Statement

A box of mass M = 1.0 kg is attached to the ceiling by a spring with spring constant k = 112.0 N/m. The spring has a relaxed length L = 28.0 cm. Initially the spring is compressed to a length L/2. If the box is released, at what distance below the ceiling will the box first be brought to rest by the spring?

Homework Equations

I don't know if this is correct, but I attempted to use an equation given by my teacher for an object falling onto a spring, which is like opposite of this problem.
mgh = mgy₂ + .5k(y₂)²

The Attempt at a Solution

I used the equation but pretty much went to a dead end >.<

 

[rl.bhat]

Show your calculations.