The current price of Tesla stock (TSLA) is $900 per share. An investor believes that TSLA is overpriced and decides to sell short 100 shares at the current market price. The initial margin requirement and maintenance margin requirement is 50% and 30%, respectively, of the value of the short position. For simplicity, assume that the margin account pays no interest.

1. Determine the initial balance of the investor's account - what is the value of assets, liabilities, and equity?

2. Without using any numbers, briefly explain whether the stock price should increase or decrease to bring a margin call to the investor's account.

3. The investor does have an insight Tesla stock price falls to $820 per share in one month. What is the investor's rate of return?