What type of tax has the same percentage tax rate for everyone regardless of income?

An investor purchases 500 shares of nevada industries common stock for $22.00 per share today. at t = 1 year, this investor receives a $0.42 per share dividend (which is not reinvested) on the 500 shares and purchases an additional 500 shares for $24.75 per share. at t = 2 years, he receives another $0.42 (not reinvested) per share dividend on 1,000 shares and purchases 600 more shares for $31.25 per share. at t = 3 years, he sells 1,000 of the shares for $35.50 per share and the remaining 600 shares at $36.00 per share, but receives no dividends. assuming no commissions or taxes, the money-weighted rate of return received on this investment is closest to: