$a)\left(9a^{2}bc-36a{b}^3{c}^3\right):\left(3ac\right)=$   $3ab-12b^2{c}^2$  

$b)\left(49k^3{m}^5+140k^4{m}^4-84k^5{m}^3\right):\left(-7k^3{m}^3\right)=$  

$=-7m^2-20km+12k^2$  

$c)\frac{120p^2{r}^7-90p^5{r}^5+210p^6{r}^3}{30p^2{r}^3}=$   $\left(120p^2{r}^7-90p^5{r}^5+210p^6{r}^3\right):\left(30p^2{r}^3\right)=$  

$=4r^4-3p^3{r}^2+7p^4$  

$d)\frac{1\frac{2}{3}{x}^8+2\frac{3}{4}{x}^6-1\frac{1}{5}{x}^3}{\frac{2}{3}{x}^2}=$   $\left(\frac{5}{3}{x}^8+\frac{11}{4}{x}^6-\frac{6}{5}{x}^3\right):\left(\frac{2}{3}{x}^2\right)=$  

$=\frac{5}{3}{x}^8:\frac{2}{3}{x}^2+\frac{11}{4}{x}^6:\frac{2}{3}{x}^2-\frac{6}{5}{x}^3:\frac{2}{3}{x}^2=$  

$=\frac{5}{\sout{3}}\cdot \frac{\sout{3}}{2}{x}^{8-2}+\frac{11}{4}\cdot \frac{3}{2}{x}^{6-2}-\frac{{\sout{6}}^3}{5}\cdot \frac{3}{{\sout{2}}^1}{x}^{3-2}=$    

$=\frac{5}{2}{x}^6+\frac{33}{8}{x}^4-\frac{9}{5}x$