C# Cache / API

I have mvc / c# / razor app that using the following method / class and I found out our developer put this on Views/Shared/Layoutpage.
It looks like it is called this method everytime when the page is refreshed. As a result, it is super easy to max out the API usage.

My question is: What is the best practice to use cache in c# to reduce this usage? In general, the layoutpage will be loaded as usual.
Please show me how it works in codes/c#. Thanks

 public static string GetLatitiudeByIP(string ip)
        {
            string returnValue = "34.028623";
            XmlDocument foo = new XmlDocument();
            foo.Load(String.Format("http://api.ipstack.com/" + ip + "?access_key=7efaasdfasdfasdfadsf3829ad25d56ab30492c9c79d24f1&output=xml&legacy=1"));
            XmlNode latitudeNode = foo.SelectSingleNode("/result/latitude");
            if(latitudeNode != null)
            {
                returnValue = latitudeNode.InnerText;
            }
            return returnValue;
        }