how to separate amount in script

I copied standard layout into zform.

amount(wrshb) is coming from standard printprogram Rfkord10.

i want to print separately total debit amount sum which is ( + ) sign

and total credit amount sum which is ( - ) sign.

the filed is Rf140-wrshb.

final i want to display difference between debit and credit amount.

debit - credit = netbalance.

how to do this in scripts.