Answer:
vₓ = g/2 x/y
Explanation:
For this exercise, let's find the time it takes for the ball on the right that has zero initial velocity to reach the ground.
y = v₀ t - ½ g t²
t = 2y / g
This is the time it takes for the ball on the right to reach the ground; at this time the ball on the left travels a distance
vₓ = x / t
vₓ = x g /2y
vₓ = g/2 x/y
Where we assume that x and y are known