Okay so first, divide 18 by 5
18/5 = 3.6
So, Jerry is doing 3.6 hours per day
then for Markus, do 21 divided by 6
21/6 = 3.5
So, Markus is working 3.5 hours each day and Jerry is working 3.6 hours each day!
That being said, Jerry is volunteering longer and he is volunteering by .1 hour longer