$a)0,2\cdot \frac{5}{6}\cdot 3=\frac{1}{6}\cdot 3=\frac{3}{6}=\frac{1}{2}$

$b)4\frac{3}{8}\cdot 3\cdot 1\frac{1}{7}=\frac{{\sout{35}}^5}{8}\cdot 3\cdot \frac{8}{{\sout{7}}^1}=$