Imagine the following scenario:

You grandfather is now confident that you can manage his money after you completed an investment course. You decide to put in practice the newly acquired knowledge by short-selling. You sell short 1200 shares of ZEUS that are currently selling at $39.1 per share. You post the 50% margin required on the short sale. What will be your rate of return per share if you sell ZEUS for $30.9? (Ignore any dividends and any interest.)