\[\frac{1}{27}x^{3} + \frac{1}{125}y^{3} =\]
\[= \left( \frac{1}{3}x + \frac{1}{5}y \right)\left( \frac{1}{9}x^{2} - \frac{1}{15}xy + \frac{1}{25}y^{2} \right).\]