Soccer ball reaches its highest position when its equation turns from positive slope to zero and then negative. Mathematically it is where the derivative of the its function equals to zero. so:
d(-3x^2 + 6x + 3) / dx = -6x + 6
-6x + 6 = 0 -> x = 1 ->
it seems Paige's ball reaches higher than Viaola's with only 6 meters height.