title: C# Linq error msg "could not find an implementation of the query pattern for source type 'double?'. 'Select' not found
body: <p>I am trying to set up a simple banking application that adds interest when the user makes a deposit. I have a textbox on the webform that accepts the deposit amount and when "Submit" is clicked the calculation will take place. however I get the "could not find an implementation of the query pattern for source type 'double?'. 'Select' not found." message in my code. Balance is declared as a double? in the Accounts class. A lot of solutions I saw already were to add the using System.Linq namespace at the top but I've already done that.</p>
  
  <pre><code>public void GetInterest()
          {
  
              var db = new CelticSavingsBank.Classes.Accounts(); 
  
              var myBalance = from a in db.Balance
                               select a;
                  db.Balance = myBalance + (myBalance * 0.03);    
  
          }
  
          protected void depositButton_Click(object sender, EventArgs e)
          {
              GetInterest();
          }
  </code></pre>