What is the change in the total North America revenue between 2018 and 2019?
{"Asia Pacific -- Travel": {"2019": 6274, "2018": 7351}, "Asia Pacific -- Local": {"2019": 216, "2018": 508}, "Asia Pacific -- Total Asia Pacific revenues": {"2019": 6490, "2018": 7859}, "Europe -- Travel": {"2019": 32081, "2018": 30856}, "Europe -- Local": {"2019": 4817, "2018": 5293}, "Europe -- Total Europe revenues": {"2019": 36898, "2018": 36149}, "North America -- Travel": {"2019": 57863, "2018": 56145}, "North America -- Local": {"2019": 10161, "2018": 11169}, "North America -- Total North America revenues": {"2019": 68024, "2018": 67314}, "Consolidated -- Travel": {"2019": 96218, "2018": 94352}, "Consolidated -- Local": {"2019": 15194, "2018": 16970}, "Consolidated -- Total revenues": {"2019": 111412, "2018": 111322}}
total_revenue_2019 = df["North America -- Total North America revenues"]["2019"]
total_revenue_2018 = df["North America -- Total North America revenues"]["2018"]
answer = total_revenue_2019 - total_revenue_2018