Question

A stone falls from a tower, height 100m.At same time another stone through with 4.5m\s velocity.when they meet and which height.

Answer 1

A stone falls from a tower, height 100m. At same time another stone through with 4.5m\s velocity. when they meet and which height.

The answer depends on a direction the second stone was thrown.
Anyhow, the first stone flight time is

t = √(2H/g) = √(2·100/9.8) ≈ 4.5175 s.

If the second stone was thrown horizonatally down, it reached the ground earlier then the first one, so the meeting time is 4.5175s and meeting height is 0m.