Classical Mechanics Problem Based On Conservation Of Energy

[KingOfDirewolves]

Homework Statement

A block of mass "m" kept on a fixed ground is connected to a spring. The spring is currently in it natural length "L". We mark a point "P" on the spring at height "0.8L". The block is of negligible height. An external force is acting on the spring such that it's acceleration is zero and after some time the point "P" reaches height "L" Find the Work done by the External Force.

Relevant Equations

None

I have tried using Conservation of Energy but I'm getting incorrect answer.

 

[BvU]

Hello your majesty, !

but I'm getting incorrect answer.

Tell us what you did to get it -- PF requires it before we can help