a: =-10/3y^2
b: \(=\dfrac{x^3\cdot16y^4\cdot z^2}{-6x^2z^2}=-\dfrac{8}{3}xy^4\)
\(-10y^3x^2:3x^2y=\left[\left(-10\right):3\right].\left(x^2:x^2\right).\left(y^3:y\right)=-\dfrac{10}{3}y^2\)
\(x^3.\left(2y\right)^4z^2:\left(-6x^2z^2\right)=\left[16:\left(-6\right)\right].\left(x^3:x^2\right).y^4.\left(z^2:z^2\right)=-\dfrac{8}{3}xy^4\)