The correct formula to calculate the profit for the buyer of a put option is:

$\text{Profit} = \text{Max}(0, X - S_T) - p_0$

Where:

• $X$ is the strike price ($210).
• $S_T$ is the stock price at expiration ($200).
• $p_0$ is the option premium paid ($9).

Substituting the values:

$\text{Profit} = \text{Max}(0, 210 - 200) - 9 = 10 - 9 = 1$

Thus, the investor's profit is $1. Options A and B are incorrect because they either miscalculate the intrinsic value or ignore it entirely.