Verse 18 returns to what the Nazirite should do. Here it refers to the ritual shaving of his or her hair.

And the Nazirite shall shave his consecrated head at the door of the tent of meeting: For shave his consecrated head, see verse 9; for the door of the tent of meeting, see verse 10.

And shall take the hair from his consecrated head and put it on the fire which is under the sacrifice of the peace offering: After the Nazirites have shaved off their hair, they must place it on the fire that burns the fellowship offering. For peace offering, see verse 14. Revised Standard Version‘s literal rendering says the Nazirites must put it on the fire which is under the sacrifice of the peace offering, which may be confusing. Good News Translation is clearer with “put it on the fire on which the fellowship offering is being burned.” Another possible model is “burn it [the hair] with the fire that consumes/destroys the fellowship offering.” There is a slight problem here since only part of the fellowship offering was burned; the next two verses make it clear that other parts of this offering were given to the priest to eat (see also Lev 7.31-38). Translators can deal with this difficulty here by saying “burn it [the hair] together with that part of the fellowship sacrifice that must be burned.”

Quoted with permission from de Regt, Lénart J. and Wendland, Ernst R. A Handbook on Numbers. (UBS Helps for Translators). Miami: UBS, 2016. For this and other handbooks for translators see here .