so the problem you're having is determining the lowest common denominator? Or is it with multiplying everything out?
Assuming the former, basically you have 3 fractions there, each with a different denominator. The easiest way to get a common denominator is to go through each fraction and multiply it by the denominators of the other two fractions. for instance for
you multiple it by and
For the second fraction, you multiple it by and
so, for the left hand side, you end up with
from here you should probably be able to see how the left side of the image you have above was created. The same process applies to the right side of the equation. I hope this was of help.