Launching a ball 1-4m with a stretched spring

[canada123]

I need to build a device that launches a small bouncy ball anywhere from 1-4m using a spring. The spring is initially compressed as much as it can be, so this device would need to work by stretching the spring somehow. I have tried to think of a few ways to do this, but have not come up with any good ideas. Do you guys have any idea how to build one? Thanks in advance for any help.

 

[Simon Bridge]

Hint - look at a slingshot: two springs, initially compressed, get stretched and released.
What are your constraints - have you been given the spring or do you get to pick one?