Números 4:29LXX

27At the appointment of Aaron and his sons shall be all the service of the sons of the Gershonites, in all their burdens, and in all their service: and ye shall appoint unto them in charge all their burdens.

28This the service of the families of the sons of Gershon in the tabernacle of the congregation: and their charge under the hand of Ithamar the son of Aaron the priest.

29As for the sons of Merari, thou shalt number them after their families, by the house of their fathers;

30From thirty years old and upward even unto fifty years old shalt thou number them, every one that entereth into the service, to do the work of the tabernacle of the congregation.

31And this the charge of their burden, according to all their service in the tabernacle of the congregation; the boards of the tabernacle, and the bars thereof, and the pillars thereof, and sockets thereof,