Парсинг определенной валюты из xml

                WebClient client = new WebClient();
                var xml = client.DownloadString("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml");
                XDocument xdoc = XDocument.Parse(xml);
                var el = xdoc.Element("Cube").Elements("Cube");
                string currency_off_USD = el.Where(x => x.Attribute("currency").Value == "USD").Select(x => x.Element("rate").Value).FirstOrDefault();
                double currency_off_USD1 = double.Parse(currency_off_USD);
                textBox6.Text = currency_off_USD1.ToString();

using (WebClient client = new WebClient())
{
    var xml = client.DownloadString("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml");
    XDocument xdoc = XDocument.Parse(xml);
    XNamespace xmlns = "http://www.ecb.int/vocabulary/2002-08-01/eurofxref";
    
    var el = xdoc.Root.Element(xmlns + "Cube").Element(xmlns + "Cube").Elements(xmlns + "Cube");
    string currency_off_USD = el.Where(x => x.Attribute("currency").Value == "USD").Select(x => x.Attribute("rate").Value).FirstOrDefault();
    double currency_off_USD1 = double.Parse(currency_off_USD, CultureInfo.InvariantCulture);
    textBox6.Text = currency_off_USD1.ToString();
}

using System.Globalization;

                WebClient client = new WebClient();
                var xml = client.DownloadString("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml");
                XDocument xdoc = XDocument.Parse(xml);
                XNamespace xmlns = "http://www.ecb.int/vocabulary/2002-08-01/eurofxref";
                var el = xdoc.Root.Element(xmlns + "Cube").Element(xmlns + "Cube").Elements(xmlns + "Cube");
                string currency_off_USD = el.Where(x => x.Attribute("currency").Value == "TRY").Select(x => x.Attribute("rate").Value).FirstOrDefault();
                double currency_off_USD1 = double.Parse(currency_off_USD, CultureInfo.InvariantCulture);
                textBox6.Text = currency_off_USD1.ToString();

var xml = XDocument.Load("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml");
var xmlns = new XmlNamespaceManager(new NameTable());
xmlns.AddNamespace("c", "http://www.ecb.int/vocabulary/2002-08-01/eurofxref");
 
var cube = xml.XPathSelectElement("//c:Cube[@currency='USD']", xmlns);
var rate = (decimal?) cube?.Attribute("rate");