How do I find the angle on the catapult?

I have to built a catapult that will travel 8 meters to hit bowling pins. But it has to go over a .4m wall that divides the 8 meters in half, 4 meters from catapult to wall and 4 meters from wall to bowling pins. I want to built a spoon catapult: a href="http://www.knightforhire.com/catapult.htm," rel="nofollow"http://www.knightforhire.com/catapult.ht…/a but I don't know how to calculate the angle at which the projectile would be launched.