What is the difference between the maximum and minimum sitting fee?
{"N Chandrasekaran, Chairman@": {"Commission": "-", "Sitting Fees": 3.6}, "Aman Mehta": {"Commission": 315.0, "Sitting Fees": 4.8}, "V Thyagarajan*": {"Commission": 100.0, "Sitting Fees": 3.0}, "Prof Clayton M Christensen**": {"Commission": 75.0, "Sitting Fees": 0.3}, "Dr Ron Sommer": {"Commission": 220.0, "Sitting Fees": 5.1}, "O P Bhatt": {"Commission": 215.0, "Sitting Fees": 7.5}, "Aarthi Subramanian@@": {"Commission": "-", "Sitting Fees": 5.7}, "Dr Pradeep Kumar Khosla": {"Commission": 150.0, "Sitting Fees": 2.1}, "Hanne Sorensen***": {"Commission": 50.0, "Sitting Fees": 0.6}, "Keki Mistry***": {"Commission": 50.0, "Sitting Fees": 0.6}, "Don Callahan****": {"Commission": 35.0, "Sitting Fees": 0.3}, "Total": {"Commission": 1210.0, "Sitting Fees": 33.6}}
max_fee = df["O P Bhatt"]["Sitting Fees"]
min_fee = df["Prof Clayton M Christensen**"]["Sitting Fees"]
answer = max_fee - min_fee