You mean make a graph with those being the x intercepts?
ax^2 + bx + c = 0
-b +- root(b^2-4ac) / 2a
= 21.4225 and 39.8262
b = -0.5 (21.4225 and 39.8262) = 30.6743
which is the midpoint between your 2 points (because the parabola is symmetrical)
since you divide by 2a, choose a = 0.5, so now you are dividing by 1.
x = 30.6743 (+ or -) root(((30.6743)^2) - 2c)
so root(((30.6743)^2) - 2c)
must be equal to the distance between b and your 2 points.
You take your larger point and subtract b, or take b and subtract your smaller point to get that.
so root(((30.6743)^2) - 2c) = 9.2518
square both sides, then subtract ((30.6743)^2) from both sides, then divide by -2 to get your answer for c.
c = 427.3795064
now you have a, b, and c for the quadratic.
y = ( 0.5x^2) - (30.6743x) + 427.3795064