Collision Detection

I’m making a Plinko-like game now, and I’ve gotten the collision down for the bottom of the screen, but how do I make it bounce off the bumpers depending on where it hits? I know how to make it bounce off the bumpers themselves, obviously, but that only makes it go in one direection. I need it to bounce realistically depending on where it hits. Can anybody help me? Thank you.

Here is the .fla: http://www.geocities.com/syphonblue/coinDrop.fla