What is the percentage change of basic earnings per share of common stock from 2018 to 2019?
{"Net income available to common stockholders": {"Dec 28, 2019": 21048.0, "Dec 29, 2018": 21053.0, "Dec 30, 2017": 9601.0}, "Weighted average shares of common stock outstandingBasic": {"Dec 28, 2019": 4417.0, "Dec 29, 2018": 4611.0, "Dec 30, 2017": 4701.0}, "Dilutive effect of employee incentive plans": {"Dec 28, 2019": 41.0, "Dec 29, 2018": 50.0, "Dec 30, 2017": 47.0}, "Dilutive effect of convertible debt": {"Dec 28, 2019": 15.0, "Dec 29, 2018": 40.0, "Dec 30, 2017": 87.0}, "Weighted average shares of common stock outstandingDiluted": {"Dec 28, 2019": 4473.0, "Dec 29, 2018": 4701.0, "Dec 30, 2017": 4835.0}, "Earnings per shareBasic": {"Dec 28, 2019": 4.77, "Dec 29, 2018": 4.57, "Dec 30, 2017": 2.04}, "Earnings per shareDiluted": {"Dec 28, 2019": 4.71, "Dec 29, 2018": 4.48, "Dec 30, 2017": 1.99}}
basic_earnings_2019 = df["Earnings per shareBasic"]["Dec 28, 2019"]
basic_earnings_2018 = df["Earnings per shareBasic"]["Dec 29, 2018"]
answer = (basic_earnings_2019 - basic_earnings_2018) / basic_earnings_2018 * 100.0