Question 47482
23,400=1260t-16t~2 or 16t~2-1260t+23,400=0 or (t-30)(t-48.75)=0 then

t=30 & t=4875 correct answe is 30 seconds.

proof 23,400=1260*30-16(30*30) or 23,400=37,800-16*900 or 
23,400=37,800-14,400 or 23,400=23,400