Quadratic formula help

Question

I'm having a hard time trying to figure this problem out, can anybody point me to the right direction or help?

An object is dropped from a height of 576 feet off the ground. The height h of the object after t seconds can be found using the equation h=576−16t^2

When will the height be 320 feet?

When will the object reach the ground?

Answer 1

If h is the height of the object dropped after t seconds, then if h = 320 ft, the time t will be the solution of

320 = 576 - 16t^2

Now get t by itself.

-256 = -16t^2. How can you get rid of the negatives?

256 = 16t^2. How do you get rid of the 16?

256/16 = 16/16 t^2

16 = t^2. What is t?

The ground is at 0 ft., so set 576 - 16t^2 = 0 and solve.