A trader writes five naked put option contracts, with each contract being on 100 shares. The option price is $10, the time to maturity is six months, and the strike price is $64.

a) What is the margin requirement if the stock price is $58?

b) How would the answer to (a) change if the rules for index options applied?

c) How would the answer to (a) change if the stock price were $75?

d) How would the answer to (a) change if the trader is buying instead of selling the options?

Please explain your answer.