\(b,\left(5xy-x^2+y\right).\dfrac{2}{5xy^2}\)
\(=5xy.\dfrac{2}{5xy^2}-x^2.\dfrac{2}{5xy^2}+y.\dfrac{2}{5xy^2}\)
\(=\dfrac{2}{y}-\dfrac{2x}{5y^2}+\dfrac{2}{5xy}\)
\(c,\left(4x^3-3xy^2+2xy\right)\left(-\dfrac{1}{3x^2y}\right)\)
\(=4x^3.\left(\dfrac{-1}{3x^2y}\right)-3xy^2.\left(\dfrac{-1}{3x^2y}\right)+2xy\left(-\dfrac{1}{3x^2y}\right)\)\(=\dfrac{-x}{3y}+\dfrac{y}{x}-\dfrac{2}{3x}\)