Finding a Target Number

Hello PaulB and Welcome to Excel Forum.
This appears to be more of a math problem than an Excel problem.
Target = (Week1 + Week2 + Week3 + Week4)/4 so;
6.5 = (9.61 + 6.65 + 7.74 + Week4)/4 so;
4 x 6.5 = 9.61 + 6.65 + 7.74 + Week4 so;
26 = 9.61 + 6.65 + 7.74 + Week4 so;
26 - 9.61 - 6.65 - 7.74 = Week4 therefore;
2 = Week4
If the values of weeks 1, 2 and 3 are known then you could use the following formula to find the value of week 4:
4 x Target - value week1 - value week2 - value week3 = value week4
It would help to see the spreadsheet set up before trying to be more specific.
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