a stone dropped from the roof at a velocity of 6m/s2 and reaches the ground with the velocity of 18m/s.how high is the roof from the ground

2 answers

use
v1²-v0²=2gS
where S is the height of the roof, g=acceleration due to gravity, v0 and v1 are initial and final velocities.
6 m/s^2 is not a velocity. You must have meant 6 m/s.

mathmate is correct. The answer will not depend upon the angle that the stone was thrown. The time the stone is in the air WILL depend upon that angle.