'Usage

Dim instance As Webs
Dim pageUrl As String
Dim returnValue As String

returnValue = instance.WebUrlFromPageUrl(pageUrl)

'Declaration

<SoapDocumentMethodAttribute("http://schemas.microsoft.com/sharepoint/soap/WebUrlFromPageUrl", RequestNamespace:="http://schemas.microsoft.com/sharepoint/soap/", ResponseNamespace:="http://schemas.microsoft.com/sharepoint/soap/", Use:=SoapBindingUse.Literal, ParameterStyle:=SoapParameterStyle.Wrapped)> _
Public Function WebUrlFromPageUrl ( _
    pageUrl As String _
) As String

Dim webService As New Web_Reference_Folder_Name.Webs()
webService.Credentials = System.Net.CredentialCache.DefaultCredentials

Dim strPageUrl As String = "http://Server_Name/sites/Site_Name/Lists/Events/AllItems.aspx"

Dim strSiteUrl As String = webService.WebUrlFromPageUrl(strPageUrl)

MessageBox.Show(strSiteUrl)