Numbers 4:28-30

Young's Literal Translation

²⁸ This [is] the service of the families of the sons of the Gershonite in the tent of meeting; and their charge [is] under the hand of Ithamar son of Aaron the priest.

²⁹ `The sons of Merari, by their families, by the house of their fathers, thou dost number them;

³⁰ from a son of thirty years and upward even unto a son of fifty years thou dost number them, every one who is going in to the host, to do the service of the tent of meeting.