Question 91225
When the object hits the ground, the height, h, will be zero. So if you set the formula for h equal to zero and solve for the time, t, this will tell you how long it will take for the object to hit the ground.

h = 16t + 784 ...but I think you may have a typo here! It should be:
{{{h = -16t^2 + 784}}} So, set this = 0 and solve for t.
{{{0 = -16t^2+784}}} Add {{{16t^2}}} to both sides.
{{{16t^2 = 784}}} Divide both sides by 16.
{{{t^2 = 49}}} Take the square root of both sides.
{{{t = 7}}} or {{{t = -7}}} Discard the negative solution as the time, t, should be a positive value.
It will take the object 7 seconds to hit the ground.