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