Using variables in formulas/ranges

Note: I am pretty new to this, so forgive my mistakes.

I have a worksheet that changes every month. New rows are added or subtracted, so I need to use variables to select ranges.

I have been trying to use variables to select a certain range in another worksheet so I can use it in another worksheet. The code is below. I am getting errors at these two spots:

Let netincome = jan & inloss & ":" & jan & inloss

 ActiveCell.Formula = "=sum('Local Results-F'!" & netincomerange & ")"

Any help is appreciated.

Dim jan As String
        
        With Cells.Find(What:="January", After:=ActiveCell, LookIn:= _
        xlFormulas, LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:= _
        xlNext, MatchCase:=False, SearchFormat:=False).Activate
        End With
        
        jan = ActiveCell.Column
    
        Application.Workbooks("88888.xlsx").Close False
        
     ''NET INCOME

    Sheets("Consolidated-F").Activate
    
    With Cells.Find(What:="Net Income (Loss)", After:=ActiveCell, LookIn:= _
    xlFormulas, LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:= _
    xlNext, MatchCase:=False, SearchFormat:=False).Activate
    End With

    netinloss = ActiveCell.Row
    
    Dim netincomerange As Range
    
    Let netincome = jan & inloss & ":" & jan & inloss

   Set netincomerange = Range(netincome)
    
    Range("C" & netinloss).Activate
    ActiveCell.Formula = "=sum('Local Results-F'!" & netincomerange & ")"
    
        End Sub