A stone is thrown vertically upward from a bridge 30.0m high at an initial velocity of 15.0 m/s . How long will it take for the stone to hit water?

I set it up first by writing my givens down:

initial velocity = 15.0 m/s.

distance (x) = 30 m ( i'm not sure if its positive or negative since its coming back down)

Acceleration = -9.8 m/s squared (negative because its force coming down against gravtiy)

used kinematic equation : X= Intial velocity (time) + 1/2 at squared

i'm not getting the answer 4.44 that im supposed to be getting..pleast help