The formula d=16t squared represents the approximant distance d in feet a skydiver falls in t seconds before opening the parachute. The formula assumes that there is no air resistance. How long does it take a skydiver take to fall 816 feet before opening the parachute?
First - you should learn the formula d = (1/2)gt2 = (1/2)(32ft/s2)(t2)
Using the formula d=16t hides the physics of what is really happening.
The 32 (or 32.2) feet per seconds squared is the acceleration caused by gravity near the earths surface.
The formula you gave does not work everywhere in the universe - d = (1/2)gt2 works everywhere in the universe.
SO to your problem...
You need to solve the formula for the unknown T.
d = (1/2)gt2 multiply both sides by 2
2d = gt2 divide both sides by g
2d/g = t2 take the square root of both sides
√(2d/g) = t switch it awound to get the unknown on the left
t = √(2d/g) now just plug in the numbers and calculate
t = √ [ 2(816 ft)/32 ft/s2 ] =