Just divide 100% by 80% and multiply that answer by 5. I'm pretty sure that's how you do it.
A parabola with an equation, y2 = 4ax has its vertex at the origin and opens to the right.
It's not just the '4' that is important, it's '4a' that matters.
This type of parabola has a directrix at x = -a, and a focus at (a, 0). By writing the equation as it is, the position of the directrix and focus are readily identifiable.
For example, y2 = 2.4x doesn't say a great deal. Re-writing the equation of the parabola as y2 = 4*(0.6)x tells us immediately that the directrix is at x = -0.6 and the focus is at (0.6, 0)
