(at maximum height), since this is the parabolic path of a projectile. So you have an unknwn velocity at maximum height, , an, unknown initial velocity, , and an unknown angle , which you need to find. I'd say there isn't enough information to find it. if you are assuming gravity of , and have the final velocity, the launch and impact heights, then you could plug in the values for x and y, and solve simultaneous equations using the equations of motion.