$2a^{-5}{b}^2\ast 3a^{-2}{b}^{-5}=(2\ast 3)a^{-5-2}{b}^{2-5}=6a^{-7}{b}^{-3}$

$(\frac{1}{2}m{n}^{-3}{)}^{-2}=(\frac{1}{2}{)}^{-2}{m}^{-2}{n}^{-3\ast (-2)}=2^2{m}^{-2}{n}^6=4m^{-2}{n}^6$

$\frac{3,6a^{2}b}{0,9a^3{b}^{-3}}=\frac{4b^{1-(-3)}}{a}=\frac{4b^{1+3}}{a}=\frac{4b^4}{a}$

$0,8a^{-6}{b}^8\ast 5a^{10}{b}^{-8}=(0,8\ast 5)a^{-6+10}{b}^{8-8}=4a^4{b}^0=4a^4$

$\frac{25x^{-3}}{y^{-4}}\ast \frac{y^4}{5x^{-7}}=\frac{25y^4}{x^3}\ast \frac{x^7{y}^4}{5}=\frac{5y^4}{1}\ast \frac{x^4{y}^4}{1}=5x^4{y}^8$

$28c^3{d}^{-2}\ast (2c{d}^{-1}{)}^{-2}=28c^3{d}^{-2}\ast \frac{c^{-2}{d}^2}{2^2}=\frac{28c^{3-2}{d}^{-2+2}}{4}=\frac{7c^1{d}^0}{1}=7c$