Excel Merge

I have inventory data being pulled from Quicken Enterprise into three spreadsheets, 1st sheet "Inventory" contains the inventory item (unique key field), inventory location, qty of on hand inventory. 2nd sheet "Sales" contains inventory item (unique key field), sales qty by month subtotaled by location. 3rd sheet "Purchase Orders" contains inventory item (unique key field), qty of item on order, vendor name, and date of ETA. I need to combine data into one spreadsheet that combines all information for each inventory item with two calculated columns that take an start date and end date, calculate the number of weekdays including holidays between the start and end date, and then to calculate the average daily sale of each item and the days of inventory on hand.