If a ping pong ball falls from the top of a building that is 168 ft High how many seconds will it take the ball to hit the ground remember the formula for distance is d = 16 ft 2
so use the formula, though you have mangled it ...
16t^2 = 168
t^2 = 168/16
...
because g = 32 ft/s^2
and d = 1/2 gt^2