$\text{a)}2\frac{2}{3}\cdot 3\frac{3}{4}=\frac{{\sout{8}}^2}{{\sout{3}}^1}\cdot \frac{{\sout{15}}^5}{{\sout{4}}^1}=2\cdot 5=10$  

$\text{b)}12\frac{4}{5}\cdot 2\frac{3}{16}=\frac{{\sout{64}}^4}{{\sout{5}}^1}\cdot \frac{{\sout{35}}^7}{{\sout{16}}^1}=4\cdot 7=28$