The payoff for a call option buyer at expiration is calculated as $C_T = \text{Max}(0, S_T - X)$, where $C_T$ is the call option's value, $S_T$ is the stock price at expiration, and $X$ is the strike price. In this scenario, $S_T = 22$ and $X = 27$, so $C_T = \text{Max}(0, 22 - 27) = 0$. The premium paid ($C_0 = 4$) is not part of the payoff calculation but affects the investor's profit, which would be negative ($-4$) in this case.