Ответ:

[tex]\frac{6mn^2}{9n^3}\\\\\frac{3x-3y}{x^2-y^2}\\\\\frac{x^2-xy}{3x^2-6xy+3y^2}[/tex]

Объяснение:

[tex]\frac{m}{3n}=\frac{m\cdot 6n^2}{3n\cdot 6n^2}=\frac{6mn^2}{9n^3}\\\\\\\frac{3}{x+y}=\frac{3(x-y)}{(x+y)(x-y)}=\frac{3x-3y}{x^2-y^2}\\\\\\\frac{x}{3x-3y}=\frac{x}{3(x-y)}=\frac{x(x-y)}{3(x-y)^2}=\frac{x^2-xy}{3(x^2-2xy+y^2)}=\\\\\frac{x^2-xy}{3x^2-6xy+3y^2}[/tex]