Angle that the stone is thrown off of the cliff?

[Cyosis]

Almost. You have a sign wrong, you can see this because you will need to take the root of a negative number in the form you have written down.

 

[balling12]

t= 3.54 sound about right?

 

[Cyosis]

I get t=3.555=3.6. So you have made a minor rounding error other than that it is correct.