Okay, first things first:
Apparently, I am a tired old man, too long removed from anything resembling an academical context of any kind...
However, I'm still certain I've never seen "subtraction" defined as "adding a negative number". The other way around - "adding a negative number" defined as "subtraction", yes, but subtraction is an older concept than negative numbers by some 18,000 to 20,000 years, rendering the definition claim somewhat absurd...
As for the order of addition and subtraction, I'll concede that I was mistaken - for some reason, I'd gotten the impression that the PEMDAS order consisted of six steps, as opposed to four. This is the sort of blindingly simple mistake pretty much only excessively intelligent people make - and I'll make no excuses for that; there's really no excuse for it.
Well, except, perhaps, that I wrote when in dire need of sleep.
As for the problem with the original formula, yes, we - or rather, you - already demonstrated that the problem wasn't in the order of operations or parentheses, which I already acknowledged.
Now if y'all will excuse a tired old grouch, I need my sleep.
And after that, perhaps it is high time for me to pick up a refresher course... It's been well over 15 years since I last touched a textbook.
