What was the change in the Loan Servicing Portfolio between 2017 and 2018?
{"Transaction Volume -- Dollars (in millions)": {"2019": 5954.0, "2018": 5030.0, "2017": 3767.0}, "Transaction Volume -- Percentage increase": {"2019": 18.0, "2018": 34.0, "2017": ""}, "Loan Servicing Portfolio -- Dollars (in millions, at end of period)": {"2019": 9150.0, "2018": 7341.0, "2017": 5390.0}, "Loan Servicing Portfolio -- Percentage increase": {"2019": 25.0, "2018": 36.0, "2017": ""}, "Active Merchants -- Number (at end of period)": {"2019": 17216.0, "2018": 14907.0, "2017": 10891.0}, "Active Merchants -- Percentage increase": {"2019": 15.0, "2018": 37.0, "2017": ""}, "Cumulative Consumer Accounts -- Number (in millions, at end of period)": {"2019": 3.03, "2018": 2.24, "2017": 1.57}, "Cumulative Consumer Accounts -- Percentage increase": {"2019": 35.0, "2018": 43.0, "2017": ""}}
loan_servicing_portfolio_2018 = df["Loan Servicing Portfolio -- Dollars (in millions, at end of period)"]["2018"]
loan_servicing_portfolio_2017 = df["Loan Servicing Portfolio -- Dollars (in millions, at end of period)"]["2017"]
answer = loan_servicing_portfolio_2018 - loan_servicing_portfolio_2017