\(\frac{27}{21} = \frac{9 \cdot 3}{7 \cdot 3} = \frac{9}{7}\)
\(\frac{x^2}{x} \cdot \frac{y}{y^3} = x \cdot \frac{1}{y^2} = \frac{x}{y^2}\)
\(\frac{9}{7} \cdot \frac{x}{y^2} = \frac{9x}{7y^2}\)
Ответ: \(\frac{9x}{7y^2}\)