How do I calculate these? Show steps, please!

Account Margin. You deposit $50,000 cash in a brokerage account and short sell $100,000 of stocks on margin. Later, the value of the stocks held short rises to $115,000. What is your account margin in dollars? $35,000 $85,000 $100,000 $115,000 Margin Calls. You deposit $50,000 cash in a brokerage account and purchase $100,000 of stocks on margin by borrowing $50,000 from your broker, who requires a maintenance margin of 30 percent. Which of the following is the largest value for your stock holdings for which you will still receive a margin call? $80,000 $100,000 $70,000 $60,000 Account Margin. You deposit $10,000 cash in a brokerage account and purchase $20,000 of stocks on margin by borrowing $10,000 from your broker. Later the value of your stock holdings falls to $17,500. What is your account margin in dollars? $5,000 $7,500 O $10,000 $15,000