You are a speculator who sells a put option on Hong Kong dollars for a premium of $0.021 per unit, with an exercise price of $.81. The option will not be exercised until the expiration date, if at all. If the spot rate of the Hong Kong dollar is $.77 on the expiration date, your net profit per unit is:

Give you answer as $X.xx per unit. Use 2 decimal places (with calculations and steps)