Consider a stock that currently sells for $40. Over each of the next two six-month periods, the stock will either increase by 15% or decrease by 15%. Semiannual risk-free rate is 3%. (Use risk-neutral probability approach.)

1. What is the value of a European call option on this stock with an exercise price of $36 and expiration in one year?

How would I solve this using the risk probability approach? I'm having a difficult time with the notes I have from class.