\[\boxed{\mathbf{4.}\mathbf{61}}\]
\[\textbf{а)}\ \frac{\frac{2,8}{5,7} \cdot 4\frac{3}{4} - \frac{2,3}{5,1}\ :2\frac{12}{17}}{11,07\ :4,1 + 0,7 \cdot 24} =\]
\[= \frac{\frac{28}{57} \cdot \frac{19}{4} - \frac{23}{51}\ :\frac{46}{17}}{2,7 + 16,8} =\]
\[= \frac{\frac{7}{3} - \frac{23}{51} \cdot \frac{17}{46}}{19,5} = \frac{2\frac{1}{3} - \frac{1}{6}}{19,5} =\]
\[= \frac{2\frac{1}{6}}{19,5} = \frac{13}{6}\ :\frac{195}{10} = \frac{13}{6} \cdot \frac{10}{195} =\]
\[= \frac{5}{3 \cdot 15} = \frac{1}{9}\]
\[\textbf{б)}\ \frac{(13,23 + 6,77) \cdot 0,02}{18\ :11,25} + 3,6 =\]
\[= \frac{20 \cdot 0,02}{1800\ :1125} + 3,6 =\]
\[= \frac{0,4}{1,6} + 3,6 = \frac{1}{4} + 3,6 =\]
\[= 0,25 + 3,6 = 3,85\]