How do I incorporate my own API Key into the google code below?

'Calculate Google Maps distance between two addresses Public Function GetDistance(start As String, dest As String) Dim firstVal As String, secondVal As String, lastVal As String firstVal = "http://maps.googleapis.com/maps/api/distancematrix/json?origins=" secondVal = "&destinations=" lastVal = "&mode=car&language=en-US&clientid=EntersKeyHere" Set objHTTP = CreateObject("MSXML2.ServerXMLHTTP") URL = firstVal & Replace(start, " ", "+") & secondVal & Replace(dest, " ", "+") & lastVal objHTTP.Open "GET", URL, False objHTTP.setRequestHeader "User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)" objHTTP.send ("") If InStr(objHTTP.responseText, """distance"" : {") = 0 Then GoTo ErrorHandl Set regex = CreateObject("VBScript.RegExp"): regex.Pattern = """value"".*?([0-9]+)": regex.Global = False Set matches = regex.Execute(objHTTP.responseText) tmpVal = Replace(matches(0).SubMatches(0), ".", Application.International(xlListSeparator)) GetDistance = CDbl(tmpVal) Exit Function ErrorHandl: GetDistance = -1 End Function