I understand how to solve problems with denominators that are variable only for example:

$\displaystyle (1 + x)/ (2x)$

but how does one solve a problem that has a constant integer in the denominator? For example :

$\displaystyle -1/(x+1) = 1 / (3x + 3) - 2 /(x-4)$

I dont know how to find the LCM for an equation like this to multiply on both sides.