42.5% of what = 20.57
<span>42.5% of x = 20.57
</span>
(42.5/100)*x = 20.57
42.5x / 100 = 20.57
x = 20.57 * 100 / 42.5
x = 48.4
Therefore 42.5% of 48.4 is 20.57.
Y = x2 - 3x is the quadric equation
Not sure if this is what you mean but this is what I got.
The discriminant of this equation is 49. The solutions for this equation are x=2 and x=-

I hope that helps.