\[\left( - 5\frac{3}{5} \right) \cdot \left( - 1\frac{4}{21} \right) = \frac{28 \cdot 25}{5 \cdot 21} = \frac{4 \cdot 5}{1 \cdot 3} =\]
\[= \frac{20}{3} = 6\frac{2}{3}.\]