What would be another example of a ""system"" in the real world that could serve as a metaphor for micro and macroeconomics?

Suppose that xtel currently is selling at $40 per share. you buy 500 shares using $15,000 of your own money, borrowing the remainder of the purchase price from your broker. the rate on the margin loan is 8%. a. what is the percentage increase in the net worth of your brokerage account if the price of xtel immediately changes to (a) $44; (b) $40; (c) $36? (leave no cells blank - be certain to enter "0" wherever required. negative values should be indicated by a minus sign. round your answers to 2 decimal places.) b. if the maintenance margin is 25%, how low can xtel’s price fall before you get a margin call? (round your answer to 2 decimal places.) c. how would your answer to requirement 2 would change if you had financed the initial purchase with only $10,000 of your own money? (round your answer to 2 decimal places.) d. what is the rate of return on your margined position (assuming again that you invest $15,000 of your own money) if xtel is selling after one year at (a) $44; (b) $40; (c) $36? (negative values should be indicated by a minus sign. round your answers to 2 decimal places.) e. continue to assume that a year has passed. how low can xtel’s price fall before you get a margin call? (round your answer to 2 decimal places.)