Elastic Energy and Conservation of Energy

[HelloMotto]

Homework Statement

A horizontal spring of force constant 12 N/m, is mounted at the edge of a lab bench to shoot marbles at targets on the floor 93.0cm below. A marble of mass 8.3 x 10^-3 kg is shot from the spring, which is initially compressed a distance of 4.0 cm. how far does the marble travel horizontally?

i can see how i can calculate this, but I am not sure what the energy statement is in this question

originally i stated that

Eelastic + Eg = Ek

but that didnt work

I tried Eelastic = Ek
and that worked.

but it dosent make sense why Eelastic + Eg = Ek dosent work.
initially the ball is off on a table. so there should be gravitational potential energy...but why dosent it work with calculation?

 

[Kurdt]

The following page may help you.

http://hyperphysics.phy-astr.gsu.edu/Hbase/pespr.html