At time t=0, in seconds, a pair of sunglasses is dropped from the Eiffel Tower in Paris. At time t, its height in feet above the ground is given by h(t)=−16t^2+1000.

Question

At time t=0, in seconds, a pair of sunglasses is dropped from the Eiffel Tower in Paris. At time t, its height in feet above the ground is given by h(t)=−16t^2+1000. 
When do the sunglasses hit the ground? Include units in your answer.
I got that the height is 1000ft and I have tried factoring it but I am not sure where to go now. I can't figure out how to set it up.

Steve · Answer

when it hits the ground, the height is zero. So, just solve -16t^2 + 1000 = 0 16(62.5-t^2) = 0 t = √62.5 = 7.9