I am currently confused about these questions. please help me to figure out these questions. thanks

Resources e that a stock is priced at $25 and pays an annual dividend of SI per share A . Assume that an investor purchases the stock paying 100% cash . After one year , the investor sells the stock for $32 . 75 per share ( after collecting the dividend ) . The percentage return on this investment was B . Assume that an investor purchases the stock on margin , paying $15 per share and borrowing the remainder from the brokerage firm with a 10 % annual interest rate After one year , the investor sells the stock for $32.75 per share ( after collecting the dividend ) . The percentage return on this investment was C . If the market is efficient , will any rational investor buy stocks on margin ? If so , which investors will do this ? If not , why not