Une formule pour 3 inconnue ?

Sub PLNE()
Dim a As Integer
Dim b As Integer
Dim c As Integer

a_1 = [$B$1]
b_1 = [$D$1]
c_1 = [$F$1]
Total = [$H$1]

a_lim = Int(Total / a_1)
b_lim = Int(Total / b_1)
c_lim = Int(Total / c_1)

lig = 4
Range("$B$" & lig & ":$F$" & Range("$B$" & lig).End(xlDown).Row).Select
Selection.ClearContents
Range("$B$" & lig).Select

For a = 0 To a_lim
    For b = 0 To b_lim
        If a * a_1 + b * b_1 > Total Then
            b = b_lim
        Else
            For c = 0 To c_lim
                If a * a_1 + b * b_1 + c * c_1 > Total Then
                    c = c_lim
                Else
                    If Abs(a * a_1 + b * b_1 + c * c_1 - Total) < 0.00000000000001 Then
                        Cells(lig, 2) = a: Cells(lig, 4) = b: Cells(lig, 6) = c
                        lig = lig + 1
                    End If
                End If
            Next
        End If

    Next
Next
End Sub