Mishpatim: Amah Ivriyah

The law is that when you buy an Amah Ivriyah (Jewish maidservant) you must give her a chance to buy her freedom. The Torah says the price she has to pay for her freedom is based on a formula. The purchase is based on a six-year contract and after each year of the contract the price to purchase her freedom is lowered by 1/6th of the amount that was originally paid for the maidservant [Shemos 21:8].

Question: Write a formula to solve for the cost to the maidservant to purchase her freedom using the following variables:  

    R= cost to the maidservant to purchase her freedom

    Y=the number of years she has been in service

    P=original contract price

Answer: P – (P * (Y/6)) = R