4-2. The following three companies reported the following financial information: Firm A: Guizhou Maotai Distillery In billion RMB Net Income 2017 2018 2019 29.01 37.83 43.97 117.41 141.88 61.06 77.20 88.85 134.61 159.85 183.04 Shareholder's Equity 96.02 (Net) Sales Total Assets Firm B: Henan Shuanghui Investment & Development Co. In billion RMB 2017 2018 2019 Net Income 4.51 5.08 5.67 Shareholder's Equity 15.47 14.00 17.12 (Net) Sales 50.58 48.93 60.35 Total Assets 23.09 22.35 28.63 Firm C: Vanke Property Company In billion RMB 2017 2018 2019 Net Income 37.21 49.27 55.13 Shareholder's Equity 186.67 235.62 270.58 (Net) Sales 242.90 297.68 367.89 Total Assets 1165.35 1528.58 1729.93 Required: a) Calculate ROE for each firm-year; disaggregate the ROE into three components based on the Dupont model. b) Summarize the main driver of ROE for each firm based on your calculation in part a). c) Evaluate whether the main driver for ROE in each case could be sustainable.