u = 352 ft/s, the vertical launch velocity
Ignore air resistance, and take g = 32 ft/s.
The stone reaches maximum height in one half the time of flight.
At maximum height, the vertical velocity is zero.
Therefore if the time to reach maximum height is t seconds, then
(352 ft/s) - (32 ft/s²)*(t s) = 0
t = 352/32 = 11 s
The time of flight is 2*t = 22 s
Answer: 22 s
