The yellow submarine was at sea level when the passengers boarded. The journey began with a descent of 40 meters. After examining the sea life, they rose 30 meters. Zach thought he saw an octopus, below. They dove again, a distance of 25 meters to watch the eight ‘legged’ sea creature.
a) Write an expression to describe the journey of the yellow submarine. _________________________________

b) At what depth did they stop to look at the octopus? ______________________