$$\frac{10a+6b}{11a^3} - \frac{6b-a}{11a^3} = \frac{10a+6b-(6b-a)}{11a^3} = \frac{10a+6b-6b+a}{11a^3} = \frac{11a}{11a^3} = \frac{1}{a^2}$$
Ответ: $$\frac{1}{a^2}$$