Suppose you have an account with a broker which requires the value of your equity in your account to be at least $42\%$ of total account value.

You have $$50,000$ to invest and you borrowed $$30,000$ on the margin from your broker for a total purchase of $$80,000$ of AMZN stock at $$200$ a share.

While you intended to hold your AMZN position for one year, however the price of the stock gradually decreases and after $3$ months to $$150.$ Then on one day it rapidly falls from $$150$ to $$82.$ What will be the cash amount of margin call your broker will ask you to deposit into your account if you do not want part of your position to be liquidated by your broker?