word problem: The height h in feet of an object after t seco

The height h in feet of an object after t seconds is given by the function:

h = –16t2 + 60t + 9

How long will it take the object to hit the ground? Round your answer to the nearest thousandth.

When it hits the ground h will be:

0 - 16t^2 + 60t + 9= 0

t = [-60+/-sqrt(3600 + 576)] - 32t = -60 + 64.62 - 32t = -27.38

Again it doesn't match any given answer. Where did I go wrong again?
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Edited by stapel -- Reason for edit: formatting

-16t^2+60t+9=0
t=-60+/-[3600 +576]^1/2 all over -32
t=-60+/-[64.62197769] all over -32
t=-124.622/-32 t=4.622/-32 can't have negative time
t=3.89 answer
Arthur

thank you soo much for your help. I figured it out though before you got this in. thank you for your effort and I appreciate it. I will need assistance next week for sure. Final assignments coming then my final in two weeks.