make me understand this part

estment In addition to the initial margin requirement, another important concept is the main nance margin, which is the required proportion of your equity to the total value of the sto after the initial transaction, The maintenance margin protects the broker if the stock pri declines. At present, the minimum maintenance margin specified by the Federal Reserve is percent, but, again, individual brokerage firms can dictate higher maintenance margins fo their customers. If the stock price declines to the point where your investor's equity drop below 25 percent of the total value of the position, the account is considered undermargined and you will receive a margin call to provide more equity. If you do not respond with the required funds in time, the stock will be sold to pay off the loan. The time allowed to meet , margin call varies between investment firms and is affected by market conditions. Under volatile market conditions, the time allowed to respond to a margin call can be shortened drastically (e.g., to one day). Given a maintenance margin of 25 percent. when you buy on margin you must consider how far the stock price can fall before you receive a margin call. The computation for our example is as follows: If the price of the stock is P and you own 200 shares, the value of your position is 200P and the equity in your account is (200P - $5,000). The percentage margin is (200P - 5,000)/200P. To determine the price, P, that is equal to 25 percent (0.25), we use the following equation: total value 200P - 5,000 200P = 0.25 200P - $5,000 = 50P 150P = $5,000 P = $33.33 Therefore, when the stock declines to $33.33, the equity value is exactly 25 percent; so if the stock declines from $50 to below $33.33, you will receive a margin call. To continue the previous example, if the stock declines further to $30 a share, its total mar- ket value would be $6,000 and your equity would be $1,000, which is only about 17 percent of the total value ($1,000/$6,000). You would receive a margin call for approximately $667, which would give you equity of $1,667, or 25 percent of the total value of the account ($1,667/$6,667) If the stock declines further, you would receive additional margin calls