Copy of a mathematical demonstration of formula for calculating customs duty (Mint 19/3/444)

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Because Merchants pretend that they are not to be taxed for the Duty they pay to the king but only the excess of the value of their goods above the Duty: for doing this the following probleme is proposed

Problem.

To lay a Duty at any assigned rate upon the excess of the value of any parcel of goods above the Duty.

Solution.

By the Rule of fals Position, assume any Excess at pleasure, & the rate will give the Duty upon it, & the Duty added to the Excess will compose the value of the goods in this case. And by the golden Rule, As this value is to the Duty, so is the Value of any parcel of goods to the Duty upon them.

Example 1

If the Excess assumed be 100li & the rate 9 per cent, the Duty will be 9li, & the value of the goods 109li. And by the golden Rule: As 109 to 9, so is the value of any parcel of Goods to the Duty upon them

Example 2

If the Excess assumed be 100li & the rate 20 per cent the Duty will be 20li & the value of the goods 120li. And by the golden Rule; As 120 to 20, so is the value of any parcel of goods to the Duty upon them.

NB. Here by the value of the goods, is to be understood the clear value which remains after the charges of warehouse room & all other charges except the Duty are subducted.