42. \(\left(1\frac{1}{5}mn\right)^2\)

\(1\frac{1}{5}=\frac{6}{5}\), поэтому \(\left(\frac{6}{5}mn\right)^2=\frac{36}{25}m^2n^2\).

Ответ: \(\frac{36}{25}m^2n^2\).