\[\left( 1\frac{1}{3}m + 3\frac{3}{5}n \right)^{2} =\]
\[= \left( \frac{4}{3}m + \frac{18}{5}n \right)^{2} =\]
\[= \frac{16}{9}m^{2} + \frac{48}{5}mn + \frac{324}{25}n =\]
\[= 1\frac{7}{9}m^{2} + 9\frac{3}{5}mn + 12\frac{24}{25}n^{2}\]