Practicing with quadratic models

1. The following two equations describe the height of a missile above (or below) the surface of the ocean, when it is launched from a submarine:

1. $ y = -t^2 + 12t - 20 $
2. $ y = -5t^2 + 30t - 20$

2. After how many seconds will each missile break through the surface of the water?
3. After ...