computing of equity reversion after taxes

does anyone know how the get the outstanding mortgage balance of409,799 in the example on p. 336, book 4? it says its face value of the loan less loan service payments reduced by interest paid. so face value was 433’125 -31’161.60 = 401’963.40… sorry, i know its probably not that important, but i hate not to know the reason why its not equal to the number above!

nobody knows?

it is unimportant