Since there's no air resistance, this is a problem in projectile motion. The goal is to find the point where the ball's parabolic trajectory intersects the incline. It is best to choose the xx-axis to be horizontal and direct to the right, the yy-axis to be vertical and direct to the up, and the origin to be at the point where the ball is fired. In the projectile equations, the launch angle α0α0 is measured from the horizontal. What is this angle in terms of θθ and ϕϕ?