Good Morning!
This modification should act on the ranges you requested. 
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
Dim userInput As String

If Target.Address Like "?[CFLIORU]*" Or Target.Address Like "$AA*" And _
     Target.Row >= 7 And Target.Cells.Count = 1 Then
    If IsNumeric(Target.Value) Then
    Do
       userInput = Application.InputBox("Low, Mid, High, or Firm", Default:="Mid", Type:=2)
       If userInput = "False" Then
            Rem Cancel pressed
           Application.EnableEvents = False
           Application.Undo
           Application.EnableEvents = True
           Exit Sub
       End If
    Loop Until userInput Like "[LMHFlmhf]*"
    Application.EnableEvents = False
    With Target
        .Range("b1").Value = Application.Proper(userInput)
    
        Select Case UCase(Left(userInput, 1))
            Case "L"
                .Range("c1") = Val(.Value) * 0.25
            Case "M"
                .Range("c1") = Val(.Value) * 0.5
            Case "H"
                .Range("c1") = Val(.Value) * 0.75
            Case "F"
                .Range("c1") = Val(.Value)
        End Select
    End With
    Application.EnableEvents = True
    End If
End If
End Sub