18 7p3q² + 14p2q3 21p2q2

18. $$ \frac{7p^3q^2 + 14p^2q^3}{21p^2q^2} = \frac{7p^2q^2(p + 2q)}{21p^2q^2} = \frac{p + 2q}{3} $$

Ответ: $$ \frac{p + 2q}{3} $$