\(M=\left(\dfrac{-2}{7}xy^2\right)^2\left(\dfrac{7}{4}x^3y^4\right)\)
\(M=\left(\dfrac{4}{49}x^2y^4\right)\left(\dfrac{7}{4}x^3y^4\right)\)
\(M=\left(\dfrac{4}{49}.\dfrac{7}{4}\right)\left(x^2.x^3\right)\left(y^4.y^4\right)\)
\(M=\dfrac{1}{7}x^5y^8\)