21. $$8 \cdot \frac{2}{5} + \frac{3}{5} =$$

$$8 \cdot \frac{2}{5} + \frac{3}{5} = \frac{8 \cdot 2}{5} + \frac{3}{5} = \frac{16}{5} + \frac{3}{5} = \frac{16+3}{5} = \frac{19}{5} = 3 \frac{4}{5}$$ Ответ: $$\frac{19}{5} = 3 \frac{4}{5}$$