Сократите дробь: a)[latex] \frac{21m}{28m}=[/latex] б)[latex] \frac{8x^3y^5}{12x^4y^3}=[/latex] в)[latex] \frac{10ab^2}{15ab}=[/latex] г)[latex] \frac{35c^2d-15fc^2}{c^3 (7d-3f)}= [/latex]