4. Упростите выражение $$c - \frac{5}{9}c + 4\frac{5}{6}c$$ и найдите его значение при $$c = 7\frac{1}{5}$$

$$c - \frac{5}{9}c + 4\frac{5}{6}c = c(1 - \frac{5}{9} + 4\frac{5}{6}) = c(\frac{9}{9} - \frac{5}{9} + \frac{29}{6}) = c(\frac{4}{9} + \frac{29}{6}) = c(\frac{4 \times 2}{9 \times 2} + \frac{29 \times 3}{6 \times 3}) = c(\frac{8}{18} + \frac{87}{18}) = c(\frac{95}{18}) = \frac{95}{18}c$$

При $$c = 7\frac{1}{5} = \frac{36}{5}$$

$$\frac{95}{18} \cdot \frac{36}{5} = \frac{95 \times 36}{18 \times 5} = \frac{19 \times 5 \times 2 \times 18}{18 \times 5} = 19 \times 2 = 38$$

Ответ: 38