Instead of using the Black-Scholes formula to estimate option values in reference to volatility, it is sometimes useful to turn the question around and back out the volatility implied in option prices. A 3-month call option with a $10 exercise price is trading for $.558, and the current stock price is $9.75. If the risk-free interest rate is 2% per 3 months (or (1.02)⁴ - 1 = .0824 per year), what is the implied volatility of the stock?