a) $$4b^2c \cdot (-2.5bc^4) = 4 \cdot (-2.5) \cdot b^2 \cdot b \cdot c \cdot c^4 = -10b^3c^5$$
б) $$(-2x^{10}y^6)^4 = (-2)^4 \cdot (x^{10})^4 \cdot (y^6)^4 = 16x^{40}y^{24}$$
в) $$(x^4)^7 = x^{4 \cdot 7} = x^{28}$$
г) $$(3x^6)^3 = 3^3 \cdot (x^6)^3 = 27x^{18}$$
Ответ: a) $$-10b^3c^5$$, б) $$16x^{40}y^{24}$$, в) $$x^{28}$$, г) $$27x^{18}$$