Or maybe I misunderstood. Do you need a Worksheet change event?

I gave the Range B5 to B455 the name InputRange (Insert, Name, Define)
specify name and range

B2 I name Rate

Then right_click the Sheet Name tab and select View Code copy the following
code into the worksheet code sheet.

Sub worksheet_Change(ByVal target As Excel.Range)
Dim VRange As Range, cell As Range
Set VRange = Range("InputRange"): Set r = Range("Rate")
For Each cell In target
 If Union(cell, VRange).Address = VRange.Address Then
   Range("B4") = WorksheetFunction.Round(cell * r, 2)
   Exit Sub
 End If
Next cell
End Sub

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Regards
Peter