What are the total deferred revenues for both 2018 and 2019?
{"Deferred license fees revenues": {"2019": 28, "2018": "$-"}, "Deferred NRE revenues": {"2019": 20, "2018": "-"}, "Deferred AirBar revenues": {"2019": 6, "2018": 59}, "Deferred sensor modules revenues": {"2019": 13, "2018": 16}, "": {"2019": 67, "2018": 75}}
total_deferred_revenues_2019 = df[""]["2019"]
total_deferred_revenues_2018 = df[""]["2018"]
answer = total_deferred_revenues_2019 + total_deferred_revenues_2018