A European call option on a non-dividend-paying stock, maturing in six months, has a price of $9 for a strike price of $50, and a price of $10 for a strike price of $55. A European put option on the same stock, with the same maturity, has a price of $7 for a strike price of $50, and a price of $6 for a strike price of $55.

Is this market arbitrage-free?

If you believe it is, please explain your answer in detail.

If you believe it is not, what arbitrage opportunity(ies) would you undertake? Build your portfolio, show the possible cash flows at the beginning and end of the period, and explain the possible profit.