Simple kinematics question -- dropping a stone down a well

[Mr Davis 97]

Homework Statement

[/B]
A boy drops a 0.10 kg stone down a 150 m well and listens for the echo. If the speed of sound is 343 degrees Celsius, the how long after the stone is dropped will the boy hear the echo?

Homework Equations

v = d/t

v² = v² + 2ax

The Attempt at a Solution

[/B]
What I did was use v² = v² + 2ax to find the velocity of the rock at the end of the well. Then I used v = at to find how long it takes to go from zero to that final velocity. Therefore, I found that the time it took to get to the end of the well was 5.53 s. Next I used t = d / v to find how long it took the sound to travel back, which is .437 s. Thus, adding these together, I got 6 s, rounded to sig figs. Is this answer correct?

 

[Doc Al]

Looks good to me.