Question 77320
If we let h=0 then we get

{{{0=176-16t^2}}}

Now rearrange the quadratic in descending order

{{{-16t^2+176=0}}}

Now use the quadratic formula to solve for t:

*[invoke quadratic "t", -16, 0, 176 ]


We must disregard the negative answer (a negative time doesn't make any sense), so our answer is 

t=3.3166

So it takes about 3.3 seconds for the rock to hit the ground