б) \frac{3}{5}n = 2\frac{7}{10} - \frac{3}{5};

б) Решим уравнение:

$$\frac{3}{5}n = 2\frac{7}{10} - \frac{3}{5}$$

$$\frac{3}{5}n = \frac{27}{10} - \frac{3}{5}$$

$$\frac{3}{5}n = \frac{27 - 3 \cdot 2}{10}$$

$$\frac{3}{5}n = \frac{27 - 6}{10}$$

$$\frac{3}{5}n = \frac{21}{10}$$

$$n = \frac{21}{10} : \frac{3}{5}$$

$$n = \frac{21}{10} \cdot \frac{5}{3}$$

$$n = \frac{7}{2} \cdot \frac{1}{1}$$

$$n = \frac{7}{2} = 3\frac{1}{2}$$

Ответ: $$3\frac{1}{2}$$