Question 1158307
Note, I am assuming you meant s=-16t^2+224t

720=-16t^2+224t
16t^2-224t+720=0
divide by 16
t^2-14t+45=0
(t-9)(t-5)=0
when t= 5 and 9 seconds

{{{graph(300,300,-10,12,-100,1000,720,-16x^2+224x)}}}