Consider a European call option on a non-dividend paying stock with an exercise price of $21 and maturity of 3 months. The current stock price is $20 and the continuously compounded risk-free rate is 12% per annum. The stock price changes by +/-10% each 3 months with equal probability. Assume there is one period to maturity and the current call price is $0.5. Is there an arbitrage opportunity? If yes, how can you exploit the arbitrage opportunity using the concept of a riskless hedge?