What is the difference between the total resources expensed for R&D in 2019 and 2018?
{"R&D expensed": {"2019": 1355, "2018": 1883}, "Capitalized software development costs": {"2019": 1074, "2018": 1276}, "Total resources expensed for R&D": {"2019": 2430, "2018": 3159}}
total_resources_2019 = df["Total resources expensed for R&D"]["2019"]
total_resources_2018 = df["Total resources expensed for R&D"]["2018"]
answer = total_resources_2019 - total_resources_2018