Answer:
Below 
Step-by-step explanation:
df = do + vo t + 1/2 a t^2 df = final position = ground = 0 
 do - original position = 75 m
 vo = 16 m/s 
 a = -9.81 m/s^2 
0 = 75 + 16 t - 1/2 ( 9.81 )t^2 
 - 4.905 t^2 + 16 t + 75 = 0 Use Quadratic Formula to find :
  t = 5.9 s