1.First you have to create unit, stock item.
2.Activate vat
3.Create sales 4%(choose sales@4%) and sales 12.5%(choose sales@12.5%) legd.
4.Create output vat4%, outputvat12.5% ledger.
5.Goto configuration(f12) chose no on common ledger A/c for item allocation.
6.Then enter sales voucher.