a: \(f\left(x\right)+g\left(x\right)=x^3-x^2+5-2x^3+x^2+2x+1=2x+6\)
\(f\left(x\right)-g\left(x\right)=x^3-x^2+5+2x^3-x^2-2x-1\)
\(=3x^3-2x^2-2x+4\)
b: \(h\left(x\right)=2\cdot f\left(x\right)-g\left(x\right)\)
\(=2\left(x^3-x^2+5\right)+2x^3-x^2-2x-1\)
\(=2x^3-2x^2+10+2x^3-x^2-2x-1\)
\(=4x^3-3x^2-2x+9\)