=IFERROR(SUM((M4:M7-M3:M6)*N3:N6*--(K9>=M4:M7))+(K9-VLOOKUP(K9;M3:M7;1))*VLOOKUP(K9;M3:N7;2);0)

Function Alsqr(tRange As Range, Range As Range) As Variant

If Range <= 0 Then Alsqr = 0: Exit Function

    Dim lr     As Long

    Dim sh     As String

    Dim rCount As Long

    Dim st     As Long

    Dim ct     As Long

    Dim i      As Long

    Dim r      As Variant

    rCount = tRange.Rows.Count

    st = tRange(1, 1).Row

    ct = tRange(1, 1).Column

    sh = tRange.Parent.Name

    lr = rCount + st

        With Sheets(sh)

        For i = st + 2 To lr - 1

        If .Cells(i, ct) < Range Then

        r = r + ((.Cells(i, ct) - .Cells(i - 1, ct)) * .Cells(i - 1, ct + 1))

        End If

        If .Cells(i, ct) >= Range Then

        r = r + ((Range - .Cells(i - 1, ct)) * .Cells(i - 1, ct + 1))

        Exit For

        End If

        Next i

        If Range > .Cells(lr - 1, ct) Then

        r = r + ((Range - .Cells(lr - 1, ct)) * .Cells(lr - 1, ct + 1))

        End If

        End With

    Alsqr = r: Exit Function

End Function