Реши уравнение 2 1/7:b=2 19/28:3 3/4.

\[2\frac{1}{7}\ :b = 2\frac{19}{28}\ :3\frac{3}{4}\]

\[\frac{15}{7}\ :b = \frac{75}{28}\ \ :\frac{15}{4}\]

\[\frac{15}{7}\ :b = \frac{75}{28} \cdot \frac{4}{15}\]

\[\frac{15}{7}\ :b = \frac{5 \cdot 15 \cdot 4}{7 \cdot 4 \cdot 15}\]

\[b = \frac{15}{7}\ :\frac{5}{7} = \frac{15}{7} \cdot \frac{7}{5}\]

\[b = \frac{15}{5} = 3.\]

\[Ответ:\ \ b = 3.\]