In the biblical Flood story, three sons of Noah entered the Ark with him.
Genesis names Noah's sons as Shem, Ham, and Japheth. Before the Flood, the narrative identifies Noah, his wife, his sons, and his sons' wives as the human family preserved aboard the ark. Thus, the number of Noah's sons aboard is three.
The three sons later receive separate attention in Genesis 9, after Noah leaves the ark. The episode involving Noah's vineyard leads to a blessing associated with Shem and Japheth and a curse concerning Canaan, the son of Ham. This later passage is also why questions about Noah's family can require careful attention to whether they ask about sons, wives, or descendants.
The answer is not the total number of people on the ark. Genesis describes eight human survivors when Noah's wife, the three sons, and the three daughters-in-law are included. The question asks only for Noah's sons.