Copy linked fields in excel spreadsheets

Hello,

I have two excel spreadsheets, that have invoice number as a common field. In sheet A, the the invoice number might repeat in 5-10 rows, once per product line. in sheet B, the invoice number is displayed only once, with shipping method. I need to link the two sheets, and copy the shipping method from the second sheet in a new column. Each line in sheet A has to have the shipping method from Sheet B