I can't get time, with formulas, help please.

Hey There,

A golf ball rolls off a horizontal cliff with an Vo speed of 11.4 m/s. The ball falls a vertical distance of 15.5 m into a lake below.

It asks a) how much time does the ball spend in the air

b) what is the speed v of the ball just before it strikes the water?

I solved for B the V as 20.82 m/s.w

I got Vo = -11.4, d = -15.5 m, a= -9.8 m/ss.

I tried every way to get time of 1.78 s using all formulas that I can and for some reason I am coming up short in time.

What am I doing wrong. Just pluncking the numbers and nothing.

HELP?

Tks