Addition and subtraction of algebraic fractions: Common nominator, then + or - numerators!

Got it !

 $\frac{a}{b} - 2\frac{a}{3b}$ $\frac{3a}{3b} - \frac{2a}{3b} = \frac{3a-2a}{3b} = \frac{a}{3b}$ $\frac{a}{x^2b} + \frac{a}{xb^3}$ $\frac{ab^2}{x^2b^3} + \frac{ax}{x^2b^3} = \frac{ab^2+ax}{x^2b^3}$ $\frac{a-b}{a^2+ab} - \frac{1}{(a+b)^2} =$ $\frac{a^2-b^2 - a}{a(a+b)^2}$