Pricing routine late delivery charges

Hi Gurus,

     Can you give solution for my requirement. My requirement is ,

I need to create Custom fields to VA31 and same has to be applicable for VA32 and VA33. As well as VA41 also.

In those Tcodes SAP provided one extra screen that is Additional data B. So need to add my Custom fields to 'Additional data B' subscreen.

This is existing SAP subscreen. And same fields has to be created in VA41 also in same subscreen.

And my another requirement is in same scenario, In VA31 condition tab i need to do some calculation by creating routine (VOFM).

For this calculation part where i should write logic.

Could anyone give me solution for adding custom fields to standard sap screen ASAP. And where i should write the logic. Thanking you

Thanks,

Satish P