Multiples of 10.
Is that what you are asking?
Check the picture below.
now, since we know what "f" is, let us use the CNT triangle with the small COR one.

I think the average spend is 11 km. i don't know for sure..
To find the height, you would do the area divided by the base, or in this case,187.5 / 25 which equals 7.5 inches. Hope this helped!