The motion in the x-axis is constant since it has no acceleration.
If you know the time it takes for the ball to fall to the ground then you can calculate the distance it travels in the x-axis. Then you have a inpact point. with coordinates from the point it rools of. Now all you need to do is make a triangel. The base is the distance in the x-axis and y-axis is the 3.5ft. And the angle is simple trigonometri. calculate the speed at impact in x-axis and y axis and there is your angle
Can you take it from here?