It's been a while but I believe you break this into two parts. The deceleration and the re acceleration of the ball vertically, using the hight it went with the force of gravity on it to find how fast it would have to start to get that high. And how long it would be in the air. Then figure how fast the ball would have to be going to go 20 ft in that amount of time. Then based on the angles you could determine the initial speed.
This may be completely wrong. It's been a very long time since I've done this
