$a)1\frac{5}{6}-2\left(\frac{9}{8}-2\frac{5}{6}\right)=$   $1\frac{5}{6}-2\cdot \frac{9}{8}+2\cdot 2\frac{5}{6}=$  

$=1\frac{5}{6}-\frac{18}{8}+4\frac{10}{6}=$   $1\frac{5}{6}-\frac{9}{4}+4\frac{5}{3}=$  

$=1\frac{5}{6}-2\frac{1}{4}+5\frac{2}{3}=$   $1\frac{5}{6}+5\frac{4}{6}-2\frac{1}{4}=$  

$=6\frac{9}{6}-2\frac{1}{4}=$   $6\frac{18}{12}-2\frac{3}{12}=$   $4\frac{15}{12}=5\frac{3}{12}$  

 

$b)\frac{3}{16}\cdot \left(-2\frac{2}{3}\right)-3\left(\frac{1}{6}+\frac{3}{4}\right)=$   $\frac{{\sout{3}}^1}{16}\cdot \left(-\frac{8}{{\sout{3}}^1}\right)-3\left(\frac{2}{12}+\frac{9}{12}\right)=$   

$=$   $-\frac{8}{16}-{\sout{3}}^1\cdot \frac{11}{{\sout{12}}^4}=$    $-\frac{1}{2}-\frac{11}{4}=$   $-\frac{2}{4}-\frac{11}{4}=$   $-\frac{13}{4}=-3\frac{1}{4}$  

$c)\left(2\frac{2}{9}-3\frac{1}{3}\right):\left(-6\frac{2}{3}\right)=$   $\left(2\frac{2}{9}-3\frac{3}{9}\right):\left(-\frac{20}{3}\right)=$   

$=\left(-\left(3\frac{3}{9}-2\frac{2}{9}\right)\right)\cdot \left(-\frac{3}{20}\right)=$   $\left(-1\frac{1}{9}\right)\cdot \left(-\frac{3}{20}\right)=$  

$=-\frac{{\sout{10}}^1}{9}\cdot \left(-\frac{3}{{\sout{20}}^2}\right)=$   $\frac{3}{9\cdot 2}=\frac{3}{18}=\frac{1}{6}$