Quadratics word problem

Question

anonymous · Answer

An arrow is shot upward from a platform 40 feet high with an initial velocity of 224 ft. per second. its height, h, in feet after t seconds is given by the equation: h= -16t^2 + 224t+40. At what times will the arrow be 824 feet above the ground?

anonymous · Answer

Am i supposed to plug in 824 for t?

anonymous · Answer

no, $t$ is the time you are looking for
you are supposed to replace $h$ by 824 and solve for $t$

anonymous · Answer

h is replaced by 824

anonymous · Answer

$$
\begin{array}{rcl}
h(t) &=& -16t^2 + 224t+40 \
824 &=& -16t^2 + 224t+40 \
0 &=& -16t^2 + 224t+40-824
\end{array}
$$
Quadratic formula.

anonymous · Answer

Ohh ok i see it now.. then you just factor, correct?

anonymous · Answer

Ummm, you're solving for $t$ here.  You can factor or use quadratic formula or whatever method you want.

anonymous · Answer

I see.. thanks!