a submarine is 450 feet below sea level. It descends 300 feet. What is its new position?

a submarine is 450 feet below sea level. It descends 300 feet. What is its new position?

We start at 450 feet below sea level. We descend another 300 feet, so we're now at:
-450 - 300 = -750

Negative depth means below sea level, so the submarine is at 750 feet below sea level