в) $$\frac{17}{42}c - \frac{2}{7}c + \frac{7}{18}c$$ при $$c = 3\frac{1}{2}; 2\frac{5}{8}$$;

в) $$\frac{17}{42}c - \frac{2}{7}c + \frac{7}{18}c$$ при $$c = 3\frac{1}{2} = \frac{7}{2}$$ и $$c = 2\frac{5}{8} = \frac{21}{8}$$;

$$\frac{17}{42}c - \frac{2}{7}c + \frac{7}{18}c = \frac{17^{(3}}{42}c - \frac{2^{(6}}{7}c + \frac{7^{(7}}{18}c = \frac{51}{126}c - \frac{12}{42}c + \frac{49}{126}c = \frac{51-36+49}{126}c = \frac{64}{126}c = \frac{32}{63}c$$

При $$c = \frac{7}{2}$$

$$\frac{32}{63} \cdot \frac{7}{2} = \frac{32 \cdot 7}{63 \cdot 2} = \frac{16 \cdot 1}{9 \cdot 1} = \frac{16}{9} = 1\frac{7}{9}$$

При $$c = \frac{21}{8}$$

$$\frac{32}{63} \cdot \frac{21}{8} = \frac{32 \cdot 21}{63 \cdot 8} = \frac{4 \cdot 1}{3 \cdot 1} = \frac{4}{3} = 1\frac{1}{3}$$

Ответ: $$1\frac{7}{9}$$ и $$1\frac{1}{3}$$