How to add range in a Formula through VBA

Dear All,

I have attached a sales tracker ,every month i have to add a range to get the the min and max value.
Now i want to automate the same min and max formula with the help of Vba .
Can any one please help me .

Dim InptboxName As String
Rows("1:1").Select
colno = Selection.Find("Min").Column
Cells(1, colno).EntireColumn.Insert
Cells(1, colno).Offset(2, 0).Select
InptboxName = InputBox("Enter the Name of Month") 'December
ActiveCell.Value = InptboxName
ActiveCell.Offset(1, 1).Select
' Automate the formula of min and max.