9514 1404 393
Answer:
 4.09 seconds
Step-by-step explanation:
The ball is in the air until h(t) = 0. Solving that equation for t, we have ...
 0 = -16t^2 +64t +6
 t^2 -4t = 3/8 . . . . . . rearrange, divide by 16
 t^2 -4t +4 = 4 3/8 . . . add 4 to complete the square
 (t -2)^2 = 4.375 . . . . write as a square
 t = 2 +√4.375 . . . . . positive square root, add 2
 t ≈ 4.09165
The ball was in the air about 4.09 seconds.