summing a range of inserted column

[Ali Balleya]

I have a workbook with Ten worksheets. Each sheet has 14 columns, with the range(d6:l7) named "subists".
With headers (Subst_1, Subst_2, Subst_3, Subst_4, Subst_5, Subst_6, Subst_7, Subst_8, Subst_9)

With range(L8:L107) Named "Subst_9". Row 108 has the columns sums

Some times I need to insert a column before range(subst_9) and fill the new column with the subst amount, and sum it in row 108.
Iused the following Macro to do this. And it works O.K for inserting the column and fill it with substAmnt.
What I need is a way to include the sum of the column at the bottom

Subists is name for range(d6:L7)
SubstName = "New_Sub"
SubstAmnt = 100

'"st" is the start row of the range to fill
'"er" is the end row of the range to fill
'"tr" is the sum row
'"I" refers to the inserted column

Worksheets(Sheet1).Select

With Worksheets(Sheet1).Names("Subists").RefersToRange
Set x = .Find(SubstName, LookIn:=xlValues)
If Not x Is Nothing Then
firstAddress = x.Address
Else
Worksheets(Sheet1).Names("Subist_L").RefersToRange.EntireColumn.Insert
Set x = .Find("", LookIn:=xlValues(
If Not x Is Nothing Then
firstAddress = x.Address
x.Value = SubstName
colCount = 1
i = x.Column
sr = 8
er = 107
tr = 108
Range(Cells(sr, i), Cells(er, i)).Value = SubstAmnt

'Ineed to insert code to put the sum in range((Cells(sr, i))
End If
End With