A pellet gun is fired straight downward from the edge of a cliff that is 15.9 m above the ground. The pellet strikes the ground with a speed of 34.3 m/s. How far above the cliff would the pellet have gone had the gun been fired straight upward?

You need to provide more information such as the muzzle velocity. Even with that info I won't be able to answer you but there are a few who will give it a good run.

I take it you know s.u.v.a.t

You mean these? SUVAT equations - Wikipedia, the free encyclopedia

Yea

use v^2=u^2+2as (twice)

yes, it can be solved easily with suvat equations.

Just checking capuchin what do you get

I get total answer 60.025