From the looks of it, it looks like "8" would be your range. Just in case you don't know the definition of the word 'range' ... It is the 'mean' of all of your output values in the particular function.
<-----------|----|-------|-------------> 7 9 15
Range: 7,15
Workout session: 15 - 7 = 8
9 would be ignored since it isn't the output part of the problem
