What was the change in the Per common share – basic from 2018 to 2019?
{"Results of Operations -- Operating revenues": {"2019": 131868.0, "2018": 130863.0, "2017": 126034.0, "2016": 125980.0, "2015": 131620.0}, "Results of Operations -- Operating income": {"2019": 30378.0, "2018": 22278.0, "2017": 27425.0, "2016": 29249.0, "2015": 30615.0}, "Results of Operations -- Net income attributable to Verizon": {"2019": 19265.0, "2018": 15528.0, "2017": 30101.0, "2016": 13127.0, "2015": 17879.0}, "Results of Operations -- Per common share  basic": {"2019": 4.66, "2018": 3.76, "2017": 7.37, "2016": 3.22, "2015": 4.38}, "Results of Operations -- Per common share  diluted": {"2019": 4.65, "2018": 3.76, "2017": 7.36, "2016": 3.21, "2015": 4.37}, "Results of Operations -- Cash dividends declared per common share": {"2019": 2.435, "2018": 2.385, "2017": 2.335, "2016": 2.285, "2015": 2.23}, "Results of Operations -- Net income attributable to noncontrolling interests": {"2019": 523.0, "2018": 511.0, "2017": 449.0, "2016": 481.0, "2015": 496.0}, "Financial Position -- Total assets": {"2019": 291727.0, "2018": 264829.0, "2017": 257143.0, "2016": 244180.0, "2015": 244175.0}, "Financial Position -- Debt maturing within one year": {"2019": 10777.0, "2018": 7190.0, "2017": 3453.0, "2016": 2645.0, "2015": 6489.0}, "Financial Position -- Long-term debt": {"2019": 100712.0, "2018": 105873.0, "2017": 113642.0, "2016": 105433.0, "2015": 103240.0}, "Financial Position -- Employee benefit obligations": {"2019": 17952.0, "2018": 18599.0, "2017": 22112.0, "2016": 26166.0, "2015": 29957.0}, "Financial Position -- Noncontrolling interests": {"2019": 1440.0, "2018": 1565.0, "2017": 1591.0, "2016": 1508.0, "2015": 1414.0}, "Financial Position -- Equity attributable to Verizon": {"2019": 61395.0, "2018": 53145.0, "2017": 43096.0, "2016": 22524.0, "2015": 16428.0}}
per_common_share_2019 = df["Results of Operations -- Per common share  basic"]["2019"]
per_common_share_2018 = df["Results of Operations -- Per common share  basic"]["2018"]
answer = per_common_share_2019 - per_common_share_2018