You observe a premium of $6.38 for a call option on Birdwell Enterprises common stock, which is currently selling for $42. The strike price on the call option is $41. The option has four months to maturity. The stock pays no dividends. The current risk-free interest rate is 2.50%. What is the implied volatility of the stock? (Round your answer to the nearest whole percent.)

Implied volatility:_____%