6. $$ \frac{30f^4g^3}{45f^7g^5} $$

Решение:

$$ \frac{30f^4g^3}{45f^7g^5} = \frac{2}{3f^{7-4}g^{5-3}} = \frac{2}{3f^3g^2} $$

Ответ: $$ \frac{2}{3f^3g^2} $$