a) $$-2ab^3 \cdot 3a^2b^4=-6a^3b^7$$
б) $$(-2a^5b^6)^3=-8a^{15}b^{18}$$
в) $$2\frac{2}{3}x^2y^3 \cdot (-1\frac{1}{2}xy^3)^4 = \frac{8}{3}x^2y^3 \cdot (\frac{3}{2})^4x^4y^{12} = \frac{8}{3} \cdot \frac{81}{16}x^6y^{15} = \frac{27}{2}x^6y^{15} = 13.5x^6y^{15}$$
Ответ: a) $$-6a^3b^7$$, б) $$-8a^{15}b^{18}$$, в) $$13.5x^6y^{15}$$