A real estate investor specializes in "flipping" rental houses (he buys a building, and turn around re-sell it for profit). He said his investment objective is "to buy at 11.0 ", and "to sell at 8.0 ", which suggests his expected gross profit margin is \%. (large positive or negative profit margin is possible) Write your answer without \%. E.g. if you answer is 21.5%, just write 21.5