A) What was the submarine's depth at the end of this rise?
First you take 4.5m/min and multiply it by 15 minutes.
Then you take the depth of the submarine which is 153 m and subtract 67.5 m to get the submarine's depth at the end of the rise.
The submarine's depth at the end of the rise was 85.5 m.
B) If the submarine continues to rise at the same rate, how much longer will it take to reach the surface?
To get how much longer it will take if the submarine continues to rise and reach the surface, you take the submarine's last depth which was 85.5 m and divide it by its first depth which was 4.5 m/min to get how many minutes it took to reach the surface.
It took 19 minutes for the submarine to reach the surface.