Numbers 4:26

22“Take a census of the sons of Gershon also, by their fathers’ houses, by their families;

23you shall count them from thirty years old and upward until fifty years old: all who enter in to wait on the service, to do the work in the Tent of Meeting.

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

25they shall carry the curtains of the tabernacle and the Tent of Meeting, its covering, the covering of sealskin that is on it, the screen for the door of the Tent of Meeting,

26the hangings of the court, the screen for the door of the gate of the court which is by the tabernacle and around the altar, their cords, and all the instruments of their service, and whatever shall be done with them. They shall serve in there.

27At 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 their duty to them in all their responsibilities.

28This is the service of the families of the sons of the Gershonites in the Tent of Meeting. Their duty shall be under the hand of Ithamar the son of Aaron the priest.

29“As for the sons of Merari, you shall count them by their families, by their fathers’ houses;

30you shall count them from thirty years old and upward even to fifty years old—everyone who enters on the service, to do the work of the Tent of Meeting.