6) -3m²n³3 -3m³n4; 464 66

6) $$\left(-\frac{3m^2n^3}{4b^4}\right)^3 : \left(-\frac{3m^3n}{b^6}\right)^4 = \frac{(-3m^2n^3)^3}{(4b^4)^3} : \frac{(-3m^3n)^4}{(b^6)^4} = -\frac{27m^6n^9}{64b^{12}} : \frac{81m^{12}n^4}{b^{24}} = -\frac{27m^6n^9}{64b^{12}} \cdot \frac{b^{24}}{81m^{12}n^4} = -\frac{27 \cdot b^{24} \cdot m^6 \cdot n^9}{64 \cdot 81 \cdot b^{12} \cdot m^{12} \cdot n^4} = -\frac{b^{12}n^5}{192m^6}$$

Ответ: $$- \frac{b^{12}n^5}{192m^6}$$