a) $$* \cdot 3a^2b^3c^5 = 15a^3b^6c^7$$
$$* = \frac{15a^3b^6c^7}{3a^2b^3c^5} = \frac{15}{3} \cdot \frac{a^3}{a^2} \cdot \frac{b^6}{b^3} \cdot \frac{c^7}{c^5} = 5a^{3-2}b^{6-3}c^{7-5} = 5ab^3c^2$$
б) $$-2a^3b^2c^7 \cdot * = -6a^5b^3c^8$$
$$* = \frac{-6a^5b^3c^8}{-2a^3b^2c^7} = \frac{-6}{-2} \cdot \frac{a^5}{a^3} \cdot \frac{b^3}{b^2} \cdot \frac{c^8}{c^7} = 3a^{5-3}b^{3-2}c^{8-7} = 3a^2bc$$
Ответ: a) $$5ab^3c^2$$, б) $$3a^2bc$$