how to convert combobox item into value and calculate it - vb.net

Question

I want to convert selected item in combobox into a number and calculate it.
I got message like this when i try to start my vb.net program.
Conversion from string "< 20 " to type 'Integer' is not valid
Any help is greatly appreciated.
this is my code:
Private Sub SaveBtn_Click(sender As Object, e As EventArgs) Handles SaveBtn.Click
Dim LHR As Integer
Dim TipeRetak As Integer
Dim LbRetak As Integer
Dim LuKer As Integer
Dim Alur As Integer
Dim Tambal As Integer
Dim Kasar As Integer
Dim amblas As Integer
Select Case ComboLHR.SelectedIndex
Case "< 20 "
LHR = 0
Case "20 - 50"
LHR = 1
Case "50 - 200"
LHR = 2
Case "200 - 500"
LHR = 3
Case "500 - 2000"
LHR = 4
Case "2000 - 5000"
LHR = 5
Case "5000 - 20000"
LHR = 6
Case "20000 - 50000"
LHR = 7
Case "> 50000"
LHR = 8
End Select
Select Case ComboTipeRetak.SelectedIndex
Case "Buaya"
TipeRetak = 5
Case "Acak"
TipeRetak = 4
Case "Melintang"
TipeRetak = 3
Case "Memanjang"
TipeRetak = 1
Case "Tidak Ada"
TipeRetak = 1
End Select
Select Case ComboLebarRetak.SelectedIndex
Case "> 2 mm"
LbRetak = 3
Case "1 - 2 mm"
LbRetak = 2
Case "< 1 mm"
LbRetak = 1
Case "Tidak Ada"
LbRetak = 0
End Select
Select Case ComboLuasKerusakan.SelectedIndex
Case "> 30%"
LuKer = 3
Case "10 - 30%"
LuKer = 2
Case "< 10%"
LuKer = 1
Case "0"
LuKer = 0
End Select
Select Case ComboKedalamanAlur.SelectedIndex
Case "> 20 mm"
Alur = 7
Case "11 - 20 mm"
Alur = 5
Case "6 - 10 mm"
Alur = 3
Case "0 - 5 mm"
Alur = 1
Case "Tidak Ada"
Alur = 0
End Select
Select Case ComboTambal.SelectedIndex
Case ">30 %"
Tambal = 3
Case "20 - 30 %"
Tambal = 2
Case "10 - 20%"
Tambal = 1
Case "< 10%"
Tambal = 0
End Select
Select Case ComboKekasaran.SelectedIndex
Case "Desintegration"
Kasar = 4
Case "Pelepasan Butir"
Kasar = 3
Case "Rough(Hungry)"
Kasar = 2
Case "Fatty"
Kasar = 1
Case "Close Texture"
Kasar = 0
End Select
Select Case ComboAmblas.SelectedIndex
Case "> 5/100 m"
amblas = 4
Case "2 - 5/100 m"
amblas = 2
Case "0 - 2/100 m"
amblas = 1
Case "Tidak Ada"
amblas = 0
End Select
Dim comand As New MySqlCommand("INSERT INTO `tb_bnkt`(`nomor`, `Nama`, `kondisi prioritas`) VALUES (#nomor,#NamaRuas,#kondisi)", Connector)
comand.Parameters.Add("#nomor", MySqlDbType.VarChar).Value = TextNomor.Text
comand.Parameters.Add("#NamaRuas", MySqlDbType.VarChar).Value = ComboNamaRuas.Text
comand.Parameters.Add("#kondisi", MySqlDbType.VarChar).Value = 17 - (Val(LHR + TipeRetak + LbRetak + LuKer + Alur + Tambal + Kasar + amblas))
If comand.ExecuteNonQuery() = 1 Then
MessageBox.Show("Data disimpan")
Loading()
TextNomor.Clear()
ComboNamaRuas.Text = String.Empty
ComboLHR.Text = String.Empty
ComboTipeRetak.Text = String.Empty
ComboLebarRetak.Text = String.Empty
ComboLuasKerusakan.Text = String.Empty
ComboKedalamanAlur.Text = String.Empty
ComboTambal.Text = String.Empty
ComboKekasaran.Text = String.Empty
ComboAmblas.Text = String.Empty
Else
MessageBox.Show("Error")
End If
End Sub

Answer 1

With simple class and data-binding you can simplify your code a little bid and get rid of current problem as well.
Public Class MyItem
Public ReadOnly Name As String
Public ReadOnly Value As Integer
Public Sub New(name As String, value As Integer)
Me.Name = name
Me.Value = value
End Sub
End Class
' Then in constructor create collection of values and bind it ot the combobox
Dim LHRValues As New List(Of MyItem) From
{
New MyItem("< 20 ", 0),
New MyItem("20 - 50", 1),
New MyItem("50 - 200", 2),
New MyItem("200 - 500", 3),
New MyItem("500 - 2000", 4),
New MyItem("2000 - 5000", 5),
New MyItem("5000 - 20000", 6),
New MyItem("20000 - 50000", 7),
New MyItem("> 50000", 8)
}
ComboLHR.DisplayMember = "Name" ' Property Name will be used as a text
ComboLHR.ValueMember = "Value" ' Property Value will be used as a value
ComboLHR.DataSource = LHRValues
' Then in the code where you need selected value
Private Sub SaveBtn_Click(sender As Object, e As EventArgs) Handles SaveBtn.Click
Dim selectedLHR As Integer = DirectCast(ComboLHR.SelectedValue, Integer)
' Other selected values
End Sub
You only need to cast ComboLHR.SelectedValue to the type you expect (Integer), because SelectedValue is of type object. I hope you have Option Strict set On.