Question 23434
height = -4.9t^2+(rate)t
   h = -4.9t^2+24.5t
Let height be 19.6 m; what is the time?
  19.6 = -4.9t^2+24.5t
  -4.9t^2+24.5t-19.6=0
This is a quadratic with a=-4.9, b=24.5, c=-19.6
*[invoke quadratic "x",-4.9,24.5,-19.6]

So, the height is 19.6 meters after 1 second
and after 4 seconds.