No problem, it happens all the time. Ok, the first thing you should do is get a LCD in the top and bottom of the larger fraction:
$\displaystyle
\frac{x + 2 - (\frac{12}{x+3})}{x - 5 + (\frac{16}{x+3})}$
The LCD in both the top and bottom will be (x+3)
So you will have a fraction over a fraction, with LCD both (x+3). Then, just multiply the top by the reciprocal of the bottom to get rid of the big fraction. This will leave you with a new fraction, which you can multiply out giving you your final LCD
Good luck!