-18p² - 8p² = ???

Someone please explain to me how this simple math question can turn into a rant. Because that's what it is going to become!
Okay, so today in fourth period, Mathematics, we are given the question...um...ok so I forgot the whole question. BUT! I remember the important part, oh how could I forget the important part! It's so important!
The important part: -18p² -8p² = +26p²
How does that work?!?!
It doesn't! Okay, so the Math teacher was wrong. Not the first time. She's not a great Math teacher and is very hard to understand, but, my point is, that answer is wrong! Someone correct me if I'm wrong but I think that is wrong!
-18, okay, now, take away another 8. So, -18, -19, -20, -21, -22, -23, -24, -25 and -26. There we go! It should be -26! Not +26!
Okay, so I went through many stages of thinking in class because I was sure I was right, but every tiny, little change made me think differently. At one stage I thought the question was: -18p² - -8p². So the answer to that would be -10p². So at that time, I was writing down -10p² everwhere! Then I looked properly and I discovered that I read the question wrong so there goes that theory.
I ended up at the beginning of my search, at -26p² or +26p²? So, call to my fellow classmates for help? Sure why not? All that came out of my mouth was undecipherable blab. I couldn't understand what I was saying and neither could they.
So, once again, back to square one, except now I have a bunch of friends wondering why I can't talk properly.
Ok. So finally I go to ask the teacher what has happened - hey I got a email...oops, off topic there. Anyway, I ask the teacher and I get halfway through my question when she walks off and explains that apparently I have been misbehaving and have been disrupting the class. All because of this one sum!
So, once again, back to square one.
I wait till class is over, and, in the most unlikely way possible, I pick up a marker, and I write: -26p², erasing the + and writing instead a -. Problem solved!
Well, that's what I thought. I still have the 'disrupting class' problem to attend...