Step by step explanation is necessary for rating. If i knew the answer i wouldn't have asked.

Suppose the initial margin m_0 = 50% and the maintenance margin m_1 = 30%. The current stock price is $100 per share, and you sell short 300 shares of the stock now. Then you will close the short position when the stock price drops to $95 or when you receive the first margin call whichever comes first. What is the probability that you can close your short position with a profit if the stock price is assumed to be a martingale? (Ignore short selling fees and interests from the proceed.) 18.14% 25.53% 65.14% 75.47% 85.47%