Ajax Post in Web forms

How to use ajax post in web forms?

 $.ajax({
                type: "POST",
                url: "frmMailRules.aspx/DeleteMailRuleItem",
                data: "{ MailRuleItemId: 104 }",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function (msg) {
                    debugger;
                    // Replace the div's content with the page method's return.
                    $("#Result").text(msg.d);
                }
            });

 <WebMethod()>
    Public Shared Function DeleteMailRuleItem(ByVal MailRuleItemId As Integer) As String

        Dim a As String = "temp"
        DeleteMailRule()
        Return a
    End Function

    Protected Sub DeleteMailRule()

    End Sub

its giving me error -

Cannot refer to an instance member of a class from within a shared method or shared member initializer without an explicit instance of the class.