\[\left( 5\frac{1}{6} \right)^{2} - \left( 7\frac{1}{3} \right)^{2} = \left( \frac{31}{6} \right)^{2} - \left( \frac{22}{3} \right)^{2} =\]
\[= \left( \frac{31}{6} \right)^{2} - \left( \frac{44}{6} \right)^{2} =\]
\[= \left( \frac{31}{6} - \frac{44}{6} \right)\left( \frac{31}{6} + \frac{44}{6} \right) =\]
\[= - \frac{7}{6} \cdot \frac{75}{6} = - \frac{7}{6} \cdot \frac{25}{2} =\]
\[= - \frac{175}{12} = - 14\frac{7}{12}.\]