Step 1: Definition of Brahmavihāra.
"Brahmavihāra" refers to mental states where a monk resides in a "divine" pure and increasingly superior abode—that is, four sublime states.
Step 2: List of individuals (Sanskrit/Pali synonyms).
(1) Maitrī (Metta)—benevolence towards all beings, loving-kindness.
(2) Karuṇā—compassion, the desire to alleviate suffering.
(3) Muditā—joy in the happiness of others, sympathetic joy.
(4) Upekṣā (Upekkhā)—equanimity, impartiality.
Step 3: Why only "4" are considered.
In the Pāli Nikāyas, these are called cār appamaññā (boundless states); traditionally, they are definitely counted as four—not three, not five/six.
Step 4: Rejection of alternatives.
Five / Six: The Brahmavihāra category does not mention this number of elements; sometimes the methods/sequences of "mettā-bhāvanā" etc. may increase, but the number four remains constant.
Three: There is no canonical form for three; making it three by excluding Upekṣā is incorrect.
Step 5: Method for remembering.
Create a phrase: “Love–Care–Cheer–Calm” = Loving-kindness, Care (Compassion), Cheer (Sympathetic Joy), Calm (Equanimity) $\Rightarrow$ total 4.
Step 6: Conclusion.
The correct answer to this question is Four; therefore, option (3) is correct.