Question

if an object is projected upward from ground level with an initial velocity of 64 ft per sec,its height h in feet t seconds later is h=-16t+64t.after how many seconds is the height 48 ft.

Answer 1

48= -16t+64t^2
put it in quadratic form:
4t^2-t-3=0
(2t-3)(2t+1)=0

so t= 3/2 second, disregard the negative answer