Option Explicit
Public Sub MoveAverage()
Dim aRange As Range
Dim i As Long
Set aRange = Range("B1:B3")
For i = 3 To 12
Cells(i, "C").Value = WorksheetFunction.Round(WorksheetFunction.Sum(aRange) / 3, 0)
Set aRange = aRange.Offset(1, 0)
Next i
End Sub