disclaimer: I'm not 100% sure if this is correct
9.66, or 10 if you rounded it up
I THINK that you add 280, 800, and 80 together to get -$1160, then divide 1160 and 30 maybe. then divide your answer with 4 to get 9.66, or 10.0
I hope this helps! if not, i am deeply sorry, friend.
,SivethTheDragon