\[\boxed{\text{5.\ 133}}\]
\[\textbf{а)}\ \frac{43,4\ :1\frac{3}{4} - 7,2 \cdot \frac{5}{6}}{55,44\ :2,1 - 17} =\]
\[= \frac{\frac{434}{10}\ :\frac{7}{4} - 1,2 \cdot 5}{26,4 - 17} =\]
\[= \frac{\frac{217}{5} \cdot \frac{4}{7} - 6}{9,4} = \frac{\frac{124}{5} - 6}{9,4} =\]
\[= \frac{24\frac{4}{5} - 6}{9,4} = \frac{18\frac{4}{5}}{9,4} = \frac{94}{5}\ :\frac{47}{5} =\]
\[= \frac{94}{5} \cdot \frac{5}{47} = 2\]
\[\textbf{б)}\ \frac{18,9\ :\frac{7}{13} - 10,5 \cdot 1\frac{3}{7}}{66,69\ :2,7 - 18} =\]
\[= \frac{18,9 \cdot \frac{13}{7} - 10,5 \cdot \frac{10}{7}}{24,7 - 18} =\]
\[= \frac{2,7 \cdot 13 - 1,5 \cdot 10}{6,7} =\]
\[= \frac{35,1 - 15}{6,7} = \frac{20,1}{6,7} = \frac{201}{67} = 3\]