Numbers 4:27

24 This is the service of the families of the Gershonites, in serving and in bearing burdens:

25 they shall bear the curtains of the tent, and the tent of meeting, its covering, and the covering of sealskin that is above on it, and the screen for the door of the tent of meeting,

26 and the hangings of the court, and the screen for the door of the gate of the court, which is by the tent and by the altar round about, and their cords, and all the instruments of their service, and whatever shall be done with them: therein shall they serve.

27 At the commandment of Aaron and his sons shall be all the service of the sons of the Gershonites, in all their burden, and in all their service; and you shall appoint to them in charge all their burden.

28 This is the service of the families of the sons of the Gershonites in the tent of meeting: and their charge shall be under the hand of Ithamar the son of Aaron the priest.

29 As for the sons of Merari, you shall number them by their families, by their fathers` houses;

30 from thirty years old and upward even to fifty years old shall you number them, everyone who enters on the service, to do the work of the tent of meeting.