I think its 2.5 km because we are trying to find out how much per hour he swam so we have to divide 7.5 by 3. 7.5 divided by 3 is 25 if 25 times 4 is 100 that means 3 times 25 is 75 then put your decimal between the 7 and the 5 our answer is 25 put your decimal between the 2 and the 5 The leatherback turtle swam 2.5 km per hour cause 3 times 2.5 is 7.5