\(Z\left(x\right)=2\left(3x^4-5x^3+x^2-\dfrac{3}{2}x-6\right)+\left(-6x^2-5x+3\right)\)
\(Z\left(x\right)=6x^4-10x^3+2x^2-3x-12-6x^2-5x+3\)
\(Z\left(x\right)=6x^4-10x^3+\left(2x^2-6x^2\right)-\left(3x-5x\right)-\left(12+3\right)\)
\(Z\left(x\right)=6x^4-10x^3-4x^2+2x-15\)