Hmm... That's hard!
Well, I ended up with 19 7/10 but I'm a bit sure its incorrect. Here's how I got my answer.
First, you look what's in the parentheses. -20 1/2. Hmm. Just that? Then look at the number outside. 4/5. Just subtract 20 1/2 and 4/5. If there was no subtraction sign, you could've just multiplied... but teachers just want to melt your brain...