For an object shot into the air, its height $h$ in feet above the ground after $t$ seconds is given by the equation $h = 80t - 16t^2$. Use this equation to answer the following questions.

1. At what times is the object on the ground?

   Hint (a):

   This is when the height is zero, or $h = 0$.

2. For what domain is this function reasonable?

   Hint (b):

   This is an object shot into the air, hence its height is always positive or $0$. For what times is $h ≥ 0$?

3. How long did it take the object to hit the ground?

   Hint (c):

   Use your answers to part (a).

4. For what times is the height greater than $64$ feet?

   Hint (d):

   Solve $80t - t^2 ≥ 64$.