A First, solve the equation

Solving will give:
5 and 1, the largest number is 5, so after 5 seconds it reaches 80 feet for the second time.
B Solve the equation

Solving gives:
t = 0 and t = 6, since it cannot hit the ground within 0 seconds, your awnser is: after 6 seconds it will hit the ground.
C Find the maximum.
Use

to find the time in seconds.
This gives: t = 3
Filling in t = 3 gives: 144 feet.
The max. height is 144 ft.