Because if that point is true than everything on that side of the number line is true. Visa versa.
I'm assuming the the numbers coming after the variables are meant to be exponents, and if I'm wrong just let me know
-3x^4 - 2x^3 + 3x^2 + 3x^4 - 4x^3 + x^2, rearrange to have like terms in order
-3x^4 +3x^4 - 2x^3 - 4x^3 +3x^2 + x^2, now simplify
0 -6x^3 + 4x^2
What weight represents 39th percentile