A put option on Walmart stock has a strike price of $550 and expires in exactly one month. Walmart is currently selling at $570 per share. The corresponding call option, with the same strike price and expiration, is trading at a premium of $27.50. According to put-call parity, if the effective monthly interest rate is 1%, what should be the per share premium on this put option contract?

a. -$51.43

b. $2.05

c. $20

d. $7.50