Answer: 47 feet
Explanation:
Originally the scuba driver was 31 feet below the surface of the water.
She then dives down a further 16 feet. The depth below the surface is now:
= 31 + 16
= 47 feet
The Scuba driver is now 47 feet below the surface of the water so if she had to come back to the surface, she would have to rise that 47 feet to get to the surface.