Since the collision is elastic, the velocity perpendicular to the incline is reversed just after the collision, thus the time of flight between any of the collisions remains same.
T=2usinθgcosα=2usin530gcos370=2√2ghgt2=2√2ghgandt4=6√2ghgs=(uxt4+12axt42)−(uxt2+12axt22)⇒s=3√2gh5×6√2ghg+gsin3702×(6√2ghg)2−⎛⎜⎝3√2gh5×2√2ghg+gsin3702×(2√2ghg)2⎞⎟⎠⇒s=112h5