13) (−2/3 xy⁴)³ =

\(\left(-\frac{2}{3}xy^4\right)^3=\left(-\frac{2}{3}\right)^3x^3y^{4\cdot3}=-\frac{8}{27}x^3y^{12}\).

Ответ: \(-\frac{8}{27}x^3y^{12}\)