What was the percentage change in product gross profit from 2018 to 2019?
{"": {"2019": "", "2018": "(dollars in millions)", "2018-2019 Dollar/Point Change": ""}, "Product gross profit": {"2019": 1105.6, "2018": 1002.5, "2018-2019 Dollar/Point Change": 103.1}, "Percent of product revenues": {"2019": 58.6, "2018": 58.0, "2018-2019 Dollar/Point Change": 0.6}, "Service gross profit": {"2019": 234.2, "2018": 217.9, "2018-2019 Dollar/Point Change": 16.3}, "Percent of service revenues": {"2019": 57.5, "2018": 58.7, "2018-2019 Dollar/Point Change": -1.2}}
product_gross_profit_2019 = df["Product gross profit"]["2019"]
product_gross_profit_2018 = df["Product gross profit"]["2018"]
answer = ( product_gross_profit_2019 - product_gross_profit_2018 ) / product_gross_profit_2018 * 100.0