I think they meant to use the concept of the time value of money, like this: https://en.wikipedia.org/wiki/Time_value_of_money#Example_2:_Present_value_of_an_a

I think they meant to use the concept of the time value of money, like this: https://en.wikipedia.org/wiki/Time_value_of_money#Example_2:_Present_value_of_an_annuity.E2.80.94solving_for_the_payment_amount https://en.wikipedia.org/wiki/Time_value_of_money#Example_2:... But their calculation was ... let's say wrong :-)