a: \(=\left(-3\cdot2\cdot\dfrac{1}{4}\right)\cdot\left(x^2\cdot x\cdot x\right)\cdot\left(y^3\cdot y\cdot y\right)=-\dfrac{3}{2}x^4y^5\)
b: \(=\left[-27\cdot\left(-\dfrac{2}{3}\right)\right]\cdot\left(x^3\cdot x^4\right)\cdot\left(y^9\cdot y\right)=18x^7y^{10}\)
c: \(=xy\left(-2+3\right)-\dfrac{2}{3}xy^2+4x^2y+12=4x^2y-\dfrac{2}{3}xy^2+xy+12\)