1)8x^2y^4*(-3x/4y^3) 2)-18x^2y^2/5ab:6xy^3/5a^2b^2 3)16a^2b^3:(-20a^5b^4/3x^2y) 4)-25x^4y^3/14m^2*(-21mn/10x^3y^2) 5)a^2-ab/b*b^2/a 6)ab+b^2/9*3a/b^2

[latex]1) 8x^2y^4*(- \frac{3x}{4y^3} )=- 6x^3y[/latex] [latex]2) - \frac{18x^2y^2}{5ab} : \frac{6xy^3}{5a^2b^2}=- \frac{18x^2y^2*5a^2b^2}{5ab*6xy^3} = - \frac{3abx}{y} [/latex] [latex]3) 16a^2b^3:(- \frac{20a^5b^4}{3x^2y} )=- \frac{16a^2b^3*3x^2y}{20a^5b^4} =- \frac{12x^2y}{5a^3b} [/latex] [latex]4)- \frac{25x^4y^3}{14m^2} *(- \frac{21mn}{10x^3y^2} )=- \frac{25x^4y^3*21mn}{14m^2*10x^3y^2}=- \frac{15nxy}{4m} [/latex] [latex]5)a^2- \frac{ab}{b} * \frac{b^2}{a}= a^{2} - b^{2} =(a-b)*(a+b)[/latex] [latex]6)ab+ \frac{b^2}{9} * \frac{3a}{b^2} = \frac{a}{3} *(3b+1)[/latex]