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