What is the percentage change in upfront fees from 2018 to 2019?
{"Upfront revenue -- Upfront fees": {"2019 $'000": 113609, "2018 $'000": 140971}, "Upfront revenue -- Click-through fees": {"2019 $'000": 3657, "2018 $'000": 1349}, "Upfront revenue -- Advertising and subscription fees": {"2019 $'000": 2161, "2018 $'000": 1604}, "Upfront revenue -- ": {"2019 $'000": 119427, "2018 $'000": 143924}, "Upfront revenue -- Trail commission revenue": {"2019 $'000": 34732, "2018 $'000": 33007}, "Upfront revenue -- Total revenue from contracts with customers": {"2019 $'000": 154159, "2018 $'000": 176931}, "Upfront revenue -- Revenue related to performance obligations satisfied in previous years": {"2019 $'000": 502, "2018 $'000": 4760}}
upfront_fees_2019 = df["Upfront revenue -- Upfront fees"]["2019 $'000"]
upfront_fees_2018 = df["Upfront revenue -- Upfront fees"]["2018 $'000"]
answer = ( upfront_fees_2019 - upfront_fees_2018 ) / upfront_fees_2018 * 100.0