Suppose an investor sells 500 shares of BSRM Inc. short at Tk. 147 per share. The broker requires an initial margin of 60% on the short position, and the investor earns 4.5% per year, compounded monthly, on the funds posted to the margin account. There is no interest paid on the proceeds of the short sale. One month later, the investor buys the same amount of shares of BSRM Inc. at Tk. 124 and returns them to the broker. The margin is released. Calculate the investor's effective annual rate of return.