The following table is a snapshot of the limit order book of stock A.

Bid		Ask
Price	Size	Price	Size
80.0	100	82.0	200
78.5	150	84.0	200
77.5	350	85.5	300
75.5	400	86.5	400
75.0	200	87.5	300

a) If a limit buy order of 600 shares at $85 comes in, how many shares will be executed? What is the average price?

b) What is the largest possible tick size of stock A?

c) Stock A is available for short sales. Simon is going to go short by making a limit sell order of 100 shares at $80. How much margin does he need to post to facilitate this trade if the initial margin requirement is 60%?

d) How can Simon close this position in (c)? What is his profit or loss (in percentage) if he closes his position in (c) at $72 later?