please explain algebra. thank you.

You purchased 100 shares of IBM common stock on margin at $70 per share. Assume the initial margin is 50% and the maintenance margin is 30%. a. Below what stock price level would you get a margin call? Assume the stock pays no dividend; ignore interest on margin. b. What would be your rate of return if you sell your stocks at the price infpart a)? c. What would be your rate of your return if you do not use buying-on-margin? d. What can you learn about buying-on-margin from this example? e. Why do people engage in buying-on-margin