Numbers 18:16 in the King James Version
And those that are to be redeemed from a month old shalt thou redeem, according to thine estimation, for the money of five shekels, after the shekel of the sanctuary, which is twenty gerahs.
Context
15 Everything that opens the womb, of all flesh which they offer to the LORD, both of man and animal, shall be yours. Nevertheless, you shall surely redeem the firstborn of man, and you shall redeem the firstborn of unclean animals.
16 You shall redeem those who are to be redeemed of them from a month old, according to your estimation, for five shekels of money, according to the shekel of the sanctuary, which weighs twenty gerahs.
17 “But you shall not redeem the firstborn of a cow, or the firstborn of a sheep, or the firstborn of a goat. They are holy. You shall sprinkle their blood on the altar, and shall burn their fat for an offering made by fire, for a pleasant aroma to the LORD.