In the case that S₀ = 100, r = 0.07, q = 0.05, sigma = 0.3, T = 1, and for an American call option with strike K = 60, at what time would a holder of the option optimally exercise?

3-step binomial tree

In the following, S₀ is the stock price in dollars as of today, K is the strike price in dollars, r is the continuously-compounded risk-free interest (as a decimal), q is the continuous dividend yield (as a decimal), sigma is the volatility (as a decimal) and T is the time to maturity in years.