Answer 1 3/5 meter below sea level
In this case, a diver goes into two different location expressed with "meters below sea level" unit. To know the distance between the two location, then you need to subtract it.
Explanation:
Distance = 2nd location - 1st location
Distance = 8 1/5 meter below sea level - 6 3/5 meter below sea level= 1 3/5 meter below sea level