a) \(4x^2y^3+2x^2y^3=\left(4+2\right)x^2y^3=6x^2y^3\)
b) \(2x^3+\left(-3x^3\right)=\left(2+\left(-3\right)\right)x^3=-x^3\)
c) \(3xy^2+5xy^2+7xy^2=\left(3+5+7\right)xy^2=15xy^2\)
d) \(6xyz+\dfrac{-1}{3}xyz+xyz=\left(6-\dfrac{1}{3}+1\right)xyz=\dfrac{20}{3}xyz\)
e) \(3x^2y^3z+\left(-2x^2y^3z\right)-4x^2y^3z=\left(3-2-4\right)x^2y^3z=-3x^2y^3z\)
f) \(25xy^2+55xy^2+75xy^2=\left(25+55+75\right)xy^2=155xy^2\)