This shouldn't even be difficult for me, but after a good 4 hours and many pages filled, I still cannot get the right answer. I got pretty close, really thought I was going to get it when everything started cancelling, but then my answer is off, although at least the correct format (took me ages to even get that lol, before then I had huge, horribly complex equations that I couldn't simplify).

This is the equation:

I need it simplified. The correct answer is:

After many hours and pages, I managed to get the following result:

So, it's at least in the right form, but my term in the denominator is out by a factor of 15, and the constant term is out by (I put it like that since 120 appears a lot when solving it).

I would really appreciate if someone can show me the correct way to simplify this, I have to be able to do this on an exam (revising at the moment).