Mass Spring Oscillator question

[LocalStudent]

Homework Statement

A mass of 0.3kg hangs motionless from a vertical spring whose length is 0.8m and unstreteched length is 0.65m.

The mass is then pulled down so the spring has the length of 0.9m and given an initial speed upwards of 1.2m/s upwards.

What is the maximum length of the spring during the subsequent motion?

The Attempt at a Solution

I started by working out the spring constant.
Fgrav = Fspring when the mass is constant
using that I got the spring constant to be 196Nm

Then after that I'm not sure what to do..

I tried working out the potential energy on the mass due to the spring. My answer for that is 24.5J

 

[Infinitum]

The idea of working out the spring constant first is correct

Now, what happens to its velocity of the block when it reaches its bottom-most point?
Then think of energy conservation of the system.

 

[LocalStudent]

Thanks, Infinitum.