What percentage of Cloud & Cognitive Software external revenue was Transaction Processing Platforms in 2019?
{"($ in millions) -- For the year ended December 31:": {"2019": 2019, "2018": 2018, "Yr.-to-Yr. Percent Change **": "Yr.-to-Yr. Percent Change **", "Yr.-to-Yr. Percent Change Adjusted for Currency **": "Yr.-to-Yr. Percent Change Adjusted for Currency **"}, "($ in millions) -- Cloud & Cognitive Software external revenue": {"2019": 23200.0, "2018": 22209.0, "Yr.-to-Yr. Percent Change **": 4.5, "Yr.-to-Yr. Percent Change Adjusted for Currency **": 6.2}, "($ in millions) -- Cognitive Applications": {"2019": 5765.0, "2018": 5633.0, "Yr.-to-Yr. Percent Change **": 2.3, "Yr.-to-Yr. Percent Change Adjusted for Currency **": 3.9}, "($ in millions) -- Cloud & Data Platforms": {"2019": 9499.0, "2018": 8603.0, "Yr.-to-Yr. Percent Change **": 10.4, "Yr.-to-Yr. Percent Change Adjusted for Currency **": 12.3}, "($ in millions) -- Transaction Processing Platforms": {"2019": 7936.0, "2018": 7974.0, "Yr.-to-Yr. Percent Change **": -0.5, "Yr.-to-Yr. Percent Change Adjusted for Currency **": 1.4}}
transaction_processing_platforms_2019 = df["($ in millions) -- Transaction Processing Platforms"]["2019"]
cloud_cognitive_software_external_revenue_2019 = df["($ in millions) -- Cloud & Cognitive Software external revenue"]["2019"]
answer = transaction_processing_platforms_2019 / cloud_cognitive_software_external_revenue_2019 * 100.0