The sentence refers to a future event on a designated date as a part of plan or arrangement. In such cases, simple present tense form or base form of verb is used.
Thus, "finish" in option B is the correct answer. This is the base form of the verb and is used to indicate the simple present tense.
"Will finish" in option A is incorrect as this indicates the simple future tense or an event that hasn't taken place as yet.
"Am finishing" in option C is incorrect as it is the present continuous form of the verb and indicates an action that is taking place at the time of speaking.
"Finished" in option D is incorrect as it indicates an action already completed or the simple past tense.