问题如下：
Daisy shorts 1800 shares of KIY company's stock on a 30% initial margin and the broker's lending rate is 2.5%. The current price is $65 per share. The broker charges a commission of $0.02 per share on sales but purchases for free. KIY stock pays an annual dividend of $1 per share. One year later, Daisy buys the 1800 shares at a price of $58 per share and close the position.Which of the following is closest to Daisy's rate of return?
选项：
A. 24.98%.
B. 24.81%
C. 32.55%.
解释：
B is correct.
Initial principal = 1800*65*0.3= 35100. The commission on sale( calculating as a part of initial cost)=1800*0.02=36
Remaining principal=1800*65*0.7=81900 ,so the first expense---lending interest=81900*2.5%=2047.5
The second expense---dividend payment=1*1800=1800, and there is no purchase commission.
The return on this investment=1800*65-1800*58-36-2047.5-1800=8716.5
Yield=8716.5/(35100+36)=24.81%
最后分母为什么要+36？ 前面一步 分子已经—36作为卖出的费用 分母为什么要（35100+36）？