Level 1

My question is multi layered; first,  I am doing the accounting and tax prep for a trust.  Within the trust there is a land contract.  One of the beneficiaries is cashing out and I need to determine the present value of the land contract to satisify the attorney and other beneficiaries.  I only have the book value (starting at the inception of the trust) and have applied the payments to principal and interest as it is paid down.  Where would I look for assistance with this computation?  Any suggestion would be appreciated.  The next step would be determining is there is a gain or loss or basis adjustment for the beneficiaries.