The problem given is below:

If we buy stock worth $1 million, and the initial margin requirements are 50%, while the maintenance margin requirement is 30%, what happens if the stock value drops by 45%?

Below this is how I worked out the problem. I am not completely sure about the maintenance margin and how to work that out.

To begin, our initial margin requirement is $500,000, which is 50% of the $1,000,000 investment.

The maintenance margin requirement is $300,000, which is 30% of the $1,000,000 investment.

If the stock price drops 45%, the loss is $450,000.

Our margin balance is now $550,000. Debt never changes, so debt is still $500,000. This means our margin is now $50,000. 30% of our $550,000 investment would now be $165,000. So $165,000 - $50,000 = $115,000 and we will get a margin call for that amount.