\(A\left(x\right)-B\left(x\right)=2x^3+4x^2-x-1-\left(2x^3-2x^2-x-3\right)\\ =2x^3+4x^2-x-1-2x^3+2x^2+x+3\\ =\left(2x^3-2x^3\right)+\left(4x^2+2x^2\right)+\left(x-x\right)+\left(3-1\right)=6x^2+2\)
A(x)+B(x)
=2x^3+4x^2-x-1+2x^3-2x^2-x-3
=4x^3+2x^2-2x-4