(a) How long does it take before it hits the water?

Use the y-information to find the time of flight. One method is to do it in two steps, first calculating the final y-velocity using the equation:

v_y ² = v_oy² + 2 a_y (y - y_o)

This gives v_y ² = 2.873² + 2 (-9.8) (-150) = 2948.3 m² / s² .
Taking the square root gives: v_y = +/- 54.30 m/s.

Remember that the square root can be positive or negative. In this case it's negative, because the y-component of the velocity will be directed down when the ball hits the ground.

Now find the time using:

v_y = v_oy + a_y t

So, -54.30 = 2.873 - 9.8 t, which gives t = 5.834 seconds.
Rounding off, the ball was in the air for 5.83 s.