Решение:

• 6) $$\frac{x}{5} - \frac{2}{5} = \frac{x-2}{5}$$
• 7) $$\frac{a}{3} + \frac{b}{3} = \frac{a+b}{3}$$
• 8) $$\frac{2a}{11} - \frac{b}{11} = \frac{2a-b}{11}$$
• 9) $$\frac{y^2}{8} - \frac{1}{8} = \frac{y^2-1}{8}$$
• 10) $$\frac{6}{x} + \frac{2}{x} = \frac{6+2}{x} = \frac{8}{x}$$
• 11) $$\frac{3a}{x} - \frac{4}{x} = \frac{3a-4}{x}$$
• 12) $$\frac{2x^2}{y^3} + \frac{x}{y^3} = \frac{2x^2+x}{y^3}$$
• 13) $$\frac{5b}{a^2} - \frac{3b}{a^2} = \frac{5b-3b}{a^2} = \frac{2b}{a^2}$$
• 14) $$\frac{x}{2y} - \frac{a}{2y} = \frac{x-a}{2y}$$
• 15) $$\frac{-2a}{b^2} + \frac{a}{b^2} = \frac{-2a+a}{b^2} = \frac{-a}{b^2}$$
• 9) $$\frac{x^2-y^2}{a} + \frac{2x^2}{a} = \frac{x^2-y^2+2x^2}{a} = \frac{3x^2-y^2}{a}$$