What was the change in ship management fees revenue from 2017 to 2018?
{"Management and administrative services revenue (i)": {"2019": 9645, "2018": 9809, "2017": 7762}, "Ship management fees revenue (ii)": {"2019": 4460, "2018": 5200, "2017": 5903}, "Interest income on short-term loan (iii)": {"2019": -109, "2018": "\u2014", "2017": "\u2014"}, "Charterhire expenses (iv)": {"2019": "\u2014", "2018": "\u2014", "2017": -17423}, "Share options expense recharge (v)": {"2019": "\u2014", "2018": "\u2014", "2017": 228}, "Interest expense on deposits payable (vi)": {"2019": "\u2014", "2018": -4779, "2017": -4622}, "Total": {"2019": 13996, "2018": 10230, "2017": -8152}}
ship_management_fees_revenue_2018 = df["Ship management fees revenue (ii)"]["2018"]
ship_management_fees_revenue_2017 = df["Ship management fees revenue (ii)"]["2017"]
answer = ship_management_fees_revenue_2018 - ship_management_fees_revenue_2017