$\displaystyle \frac{2}{6x^2} + \frac{4}{9x^3} $
I need a common denominator?
That's a good start but its not quite correct.
$\displaystyle \displaystyle \frac{2}{6x^2}+\frac{4}{9x^3} $
$\displaystyle \displaystyle \frac{2}{6x^2}\times \frac{9x^3}{9x^3}+\frac{4}{9x^3}\times \frac{6x^2}{6x^2} $
$\displaystyle \displaystyle \frac{\dots}{54x^5}+\frac{\dots}{54x^5} $