The first tranche of just issued, $1OOmillion (total principal value)CMO has a principle of $1million. The underlying mortgages in the pool all have an interest rate of 5% and the average mortgage has a principle of $500,000. Using the principle amount you just calculated, and assuming that value won't change substantially for the first couple of payments, how long will it be before this first traunche is retired assuming there are no pre-payment