4) $$(3x^6y^3)^4 \cdot (-\frac{1}{81}xy^2)$$

$$(3x^6y^3)^4 \cdot (-\frac{1}{81}xy^2) = 3^4x^{24}y^{12} \cdot (-\frac{1}{81}xy^2) = 81x^{24}y^{12} \cdot (-\frac{1}{81}xy^2) = -\frac{81}{81}x^{24+1}y^{12+2} = -x^{25}y^{14}$$

Ответ: $$-x^{25}y^{14}$$