Asubmarine was situated 760 feet below sea level. if it goes 320 feet up and then down 80 feet, what is the submarine's new position?

The submarine should be 520 feet below sea level now. 
-760 feet
So, since you're going up you subtract 760 and 320 you get 440 feet below sea level.
Then you add 80 feet since you're going below sea level. You get 520 feet below sea level.