Question 75192
h(t)=-16t^2+112t 
Let the height be 180 ft. then:
-16t^2+112t-180=0
4(-4t^2+28t-45)=0
Use the Quadratic Formula to find "t".
t=[-28+-sqrt(784-4*-4*-45)]/-8
t=[-28+-8]/-8
t=-36/-8=4.5 seconds
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Cheers,
Stan H.