A stock price is currently $100. A call option on this stock with a strike price of $100 and one year to maturity costs $13.61. The continuous-time interest rate is 5%. By using a one-step binomial tree, estimate the expected volatility level (σ) for the stock. Assume that u and d are modeled as below. 

( Excel's Goal Seek will help solving this and will be much appreciated to be posted to see how it has been used to solve this problem, thanks)

 

u = eVAr d = 1/u = e oV