credit memo

hi all,

i have these requirement.

i made SD cycle, SO -> DO -> billing.

billing use F2, with qty 10Pcs, and amount = 1000$. post to accounting.

then i want to create credit memo based on that billing (75$), but without specify any quantity of material. so i want just input the material and price to be credited ($75) in credit memo request.

how we do that?

please advice,

Best regard,

Hendry