Consider the following limit order book.

$\backslash$table$[[$Limit Buy Orders,Limit Sell Orders$],[$Price$,$Shares,Price,Shares$],[$$$120\mathrm{.}20,200,$$$120\mathrm{.}22,100],[$$$120\mathrm{.}18,400,$$$120\mathrm{.}24,200],[$$$120\mathrm{.}16,800,$$$120\mathrm{.}26,300],[$$$120\mathrm{.}14,600,$$$120\mathrm{.}27,100],[$$$120\mathrm{.}13,200,,]]$

If a market buy order for $200$ shares is placed, at what price will it be filled and what will be the total cost for the investor placing the market buy order? Fill in the first row in the table below to show what the top of the limit order book will look like after the market buy order is filled $($i$.$e$.,$ show the highest bid price and the lowest ask price along with the number of shares available at those prices$).$

$\backslash$table$[[$Limit Buy Orders,Limit Sell Orders$],[$Price$,$Shares,Price,Shares$],[$$$,1,$$$1,]]$

You purchased $500$ shares of Palantir common stock on margin at $$20$ per share. Assume that the initial margin is $50\%$ and that the maintenance margin is $30\%.$ Also assume that the stock pays no dividends and that there is no interest charged on the margin loan. Compute the critical price that triggers a margin call if the stock price falls to$,$ or below, that critical price.