\frac{?}{?}*\frac{2}{3}=\frac{2}{5}
\frac{?}{?}=\frac{2}{5}:\frac{2}{3}=\frac{2}{5}*\frac{3}{2}=\frac{6}{10}=\frac{3}{5}
…
\frac{3}{7}*\frac{?}{?}=\frac{4}{21}
\frac{?}{?}=\frac{4}{21}:\frac{3}{7}=\frac{4}{21}*\frac{7}{3}=\frac{4}{9}
…
1\frac{1}{2}*\frac{?}{?}=\frac{1}{2}
\frac{3}{2}*\frac{?}{?}=\frac{1}{2}
\frac{?}{?}=\frac{1}{2}:\frac{3}{2}=\frac{1}{2}*\frac{2}{3}=\frac{1}{3}
…
\frac{6}{7}*\frac{?}{?}=2\frac{2}{7}
\frac{6}{7}*\frac{?}{?}=\frac{16}{7}
\frac{?}{?}=\frac{16}{7}:\frac{6}{7}=\frac{16}{7}*\frac{7}{6}=\frac{16}{6}=2\frac{4}{6}=2\frac{2}{3}