3) 6\frac{2}{5} \cdot 1\frac{9}{16} - (2\frac{1}{4})^2 ;

3)

$$6\frac{2}{5} \cdot 1\frac{9}{16} - (2\frac{1}{4})^2 = \frac{32}{5} \cdot \frac{25}{16} - (\frac{9}{4})^2 = \frac{2}{1} \cdot \frac{5}{1} - \frac{81}{16} = 10 - \frac{81}{16} = \frac{160}{16} - \frac{81}{16} = \frac{79}{16} = 4\frac{15}{16}$$

Ответ: $$4\frac{15}{16}$$