Sub Extrapole()
Application.ScreenUpdating = False
N = Cells(1, Columns.Count).End(xlToLeft).Column
Range(Cells(1, "A"), Cells(10000, N)).Font.Color = vbBlack
For L = 2 To Range("B65500").End(xlUp).Row
For C = 3 To 8
If Cells(L, C) = "" Then
X10 = Cells(L, "B") - Cells(L - 1, "B")
X21 = Cells(L + 1, "B") - Cells(L - 1, "B")
Y21 = Cells(L + 1, C) - Cells(L - 1, C)
Y1 = Cells(L - 1, C)
Y = (X10 / X21) * (Y21) + Y1
Cells(L, C) = Y
Cells(L, C).Font.Color = vbRed
End If
Next C
Next L
End Sub