how to get Funds avalibility against each invoice

Dear all;

I have a requirement that my client wants to have a report which have 4 columns  invoice num,date,fund avaliable and invoice amount from eg

Invoice Num || Date            || Funds Avaliable || Invoice Amount

0001              01-JAN-2011                 100000                   10000

0002             02-JAN-2011                    90000                     5000

0003             03-JAN-2011                    85000                     3000

so can any one tell me which package should I use to get funds avaliable against each invoice or is there is other way out.

Thanks

Regards,

Kamran Chagani