these are some questions i need help solving and explanation to understand !

23. You purchased 100 shares of ABC common stock on margin at $70 per share. Assume the initial margin is 50% and the maintenance margin is 30%. Below what stock price level would you get a margin call? Assume the stock pays no dividend; ignore interest on margin. A. $27 B. $50 C. $60 D. $80 24. Regarding the previous question, if the stock price declines to $50 per share, what's the return to the investor's equity? What if the stock rises to $100 per share? Ignoring the interest and transactions costs. A. 57.1% and -85.7% B. 57.1% and 85.9% C. 57.4% and -85.7% D. -57.1% and 85.7% 25. Grott and Perrin, Inc. has expected earnings of $3 per share for next year. The firm's ROE is 20% and its eamings retention ratio is 60%. If the firm's market capitalization rate is 15%, what percentage of its share price is attributed to the present value of its growth opportunities (PVGO)? A. 78% B. 60% C. 40% D. 50% 26. XYZ Company has an expected ROE of 25%. The dividend growth rate will be if the firm follows a policy of paying 20% of earnings in the form of dividends. A) 5% B) 20% C) 25% D) 18% 27. Which of the following statements is true regarding the optimal risky portfolio: A) It is designated by the point of tangency with iso-utility curve and the capital allocation line. B) It is designated by the point of highest Sharpe ratio in the opportunity set. C) It is designed by the point of tangency with the opportunity set and the securities market line. D) This portfolio gives the highest standard deviation risk per unit of risk premium in the opportunity set