What you need to do to find the constant rate is first you take 300 divided by 2 to get how many feet a submarine dives per minute. 300/2 equals 150. The submarine dives 150 feet per minute. Since you know how many feet a submarine dives per minute, you can do 150 time 60, since there are 60 minutes in an hour. 60 times 150 equals 9,000. So a submarine dives 9,000 feet per hour and 150 feet per minute.