$$\frac{23a - 14}{18a^2} - \frac{4 + 5a}{18a^2} = \frac{23a - 14 - (4 + 5a)}{18a^2} = \frac{23a - 14 - 4 - 5a}{18a^2} = \frac{18a - 18}{18a^2} = \frac{18(a - 1)}{18a^2} = \frac{a - 1}{a^2}$$
Ответ: $$\frac{a-1}{a^2}$$