It would be easier to help if you could upload the spreadsheet from which the screen shot in post # 6 is taken, as per the directions in post #3. For one thing I can't tell if "Store #" is in cell A1 or C10 so it makes it hard to write a formula(s).
That said, assuming "Store#" is in A1, the formula for week 4 it would be: = 4*B7 - B2 - B3 - B4
or
= 4*B7 - SUM(B2:B4)
Let us know if you have any questions.