a)
\(\begin{array}{l}\dfrac{7}{3}{x^3}{y^2}:M = 7x{y^2}\\ \Rightarrow M = \dfrac{7}{3}{x^3}{y^2}:7x{y^2} = \left( {\dfrac{7}{3}:7} \right).\left( {{x^3}:x} \right).\left( {{y^2}:{y^2}} \right) = \dfrac{1}{3}{x^2}\end{array}\)
b)
\(\begin{array}{l}N:0,5x{y^2}z = - xy\\ \Rightarrow N = \left( { - xy} \right).0,5x{y^2}z = \left( { - 0,5} \right).\left( {x.x} \right).\left( {y.{y^2}} \right).z = - 0,5{x^2}{y^3}z\end{array}\)