Answer:
I believe it's 8.09 seconds, but I'm rusty on my physics.
Explanation:
The equation for solving the time it takes for an object to fall is [tex]\sqrt{2d/g}[/tex]
So multiply the distance times 2, and you get 642 meters. Then you divide by gravities acceleration constant, 9.8, and you get 65.51. Finally, [tex]\sqrt{65.51}[/tex], and you get 8.09 seconds.
I pulled the equation off of wikipedia and I'm unsure if it's the correct one, so hopefully this is correct. :/