3) $$1\frac{3}{5} \cdot \left(\frac{3}{4} + 1\frac{3}{8}\right)$$;

3) $$1\frac{3}{5} \cdot \left(\frac{3}{4} + 1\frac{3}{8}\right) = \frac{1 \cdot 5 + 3}{5} \cdot \left(\frac{3}{4} + \frac{1 \cdot 8 + 3}{8}\right) = \frac{5 + 3}{5} \cdot \left(\frac{3}{4} + \frac{8 + 3}{8}\right) = \frac{8}{5} \cdot \left(\frac{3}{4} + \frac{11}{8}\right) = \frac{8}{5} \cdot \left(\frac{3 \cdot 2}{4 \cdot 2} + \frac{11}{8}\right) = \frac{8}{5} \cdot \left(\frac{6}{8} + \frac{11}{8}\right) = \frac{8}{5} \cdot \frac{6 + 11}{8} = \frac{8}{5} \cdot \frac{17}{8} = \frac{8 \cdot 17}{5 \cdot 8} = \frac{17}{5} = 3\frac{2}{5}$$

Ответ: $$3\frac{2}{5}$$