Excel Lookup Functions Expert Needed

I am in need of assistance with Excel. Specifically, I want to VLOOKUP and match the BILLED AMOUNT in Spreadsheet #2 with the worker's Total Pay and Tax in Spreadsheet #1 for the exact same work week. I am stuck because the work periods are in different formats in each spreadsheet. I need someone to teach me how to format the similar work periods for easier lookup. There are no other unique identifiers to help with the vlookup. This is the best data that with exact columns that I have available.