excel spreadsheet help with fomula

On my excel spreadsheet I’ve got a column labeled 1 through 100 (Item#’s) and a
column with (dates).
Further over on the same spreadsheet I have the same columns located in the
middle and at the end of the spreadsheet going from left to right. Iwant to be able to type in the item # and the Date only once and have it appear in all three columns for each. Can you give me a fomula for doing this and tell me how to set it up on an existing spreadsheet.