Numbers 18:8-19

8Then the Lord spoke to Aaron, “Behold, aI have given you charge of the contributions made to me, all the consecrated things of the people of Israel. I have given them to you bas a portion and to your sons as a perpetual due. 9This shall be yours of the most holy things, reserved from the fire: every offering of theirs, every grain offering of theirs and every csin offering of theirs and every dguilt offering of theirs, which they render to me, shall be most holy to you and to your sons. 10In a most holy place shall you eat it. Every male may eat it; it is holy to you. 11This also is yours: the contribution of their gift, all the ewave offerings of the people of Israel. I have given them to fyou, and to your sons and daughters with you, as a perpetual due. gEveryone who is clean in your house may eat it. 12 hAll the best of the oil and all the best of the wine and of the grain, ithe firstfruits of what they give to the Lord, I give to you. 13The first ripe fruits of all that is in their land, jwhich they bring to the Lord, shall be yours. kEveryone who is clean in your house may eat it. 14 lEvery devoted thing in Israel shall be yours. 15 mEverything that opens the womb of all flesh, whether man or beast, which they offer to the Lord, shall be yours. Nevertheless, nthe firstborn of man you shall redeem, and the firstborn of unclean animals you shall redeem. 16And their redemption price o(at a month old you shall redeem them) you shall fix at five shekels
A  shekel was about 2/5 ounce or 11 grams
in silver, according to the shekel of the sanctuary, qwhich is twenty gerahs.
17 rBut the firstborn of a cow, or the firstborn of a sheep, or the firstborn of a goat, you shall not redeem; they are holy. You shall sprinkle their blood on the altar and shall burn their fat as a food offering, with a pleasing aroma to the Lord. 18But their flesh shall be yours, as sthe breast that is waved and as the right thigh are yours. 19 tAll the holy contributions that the people of Israel present to the Lord I give to you, and to your sons and daughters with you, as a perpetual due. uIt is a covenant of salt forever before the Lord for you and for your offspring with you.”
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