a)

$2\frac{1}{7}\underset{1}{\underbrace{\cdot }}1,6\underset{2}{\underbrace{\cdot }}2\frac{1}{3}=\frac{\sout{15}{}^3}{7}\cdot \frac{16}{\sout{10}{}_2}\cdot \frac{7}{3}=\frac{48}{\sout{14}{}_2}\cdot \frac{\sout{7}{}^1}{3}=\frac{48}{6}=8$   

b)

$2\frac{6}{11}\underset{1}{\underbrace{\text{:}}}\frac{7}{11}\underset{2}{\underbrace{\text{:}}}3,4=\frac{28}{\sout{11}{}_1}\cdot \frac{\sout{11}{}^1}{7}:\frac{34}{10}=\frac{\sout{28}{}^4}{\sout{7}{}_1}\cdot \frac{10}{34}=4\cdot \frac{5}{17}=\frac{20}{17}=1\frac{3}{17}$