Vt-4.9t^2 equation?

I am uming this is done neglecting air resistance. You have to find when the velocity is zero, the highest point and that is when Vo=at that is 294=9.8t =>t=294/9.8=30s disregarding air resistance. The max height=Vot-.5at^2 =294*30-4.9*900=4410M. 4410-2450=1960m=at=9.8t=> t=200seconds