A stock price is currently $20. It is known that in three months it will go up to 22 or down to 18. The risk-free interest rate is 6% per annum with continuous compounding. What is p (the risk-neutral probability of an up movement)? (Show full working)

a) 0.7682

'b) 0.5756

c) 0.8092

d) 0.2345