why im getting this error when im trying build and execute a radtextbox for store text in variable from input in textbox?

hi im new to this community :) why im getting this error when im trying build and execute a radtextbox for store text in variable from input in textbox?

its like same error for days i fix code everytime using bug submit but useless

can someone help :) appreciated

the error :

[ Compiler ]
18:27:31 'ERROR' > c:\Users\Administrator\Documents\Test Studio Projects\TestProject4\WebTest.tstest.cs(55,43) : error CS1061: 'Telerik.WebAii.Controls.Html.RadTextBox' does not contain a definition for 'Text' and no extension method 'Text' accepting a first argument of type 'Telerik.WebAii.Controls.Html.RadTextBox' could be found (are you missing a using directive or an assembly reference?)
18:27:31 'ERROR' > c:\Users\Administrator\Documents\Test Studio Projects\TestProject4\WebTest.tstest.cs(56,14) : error CS1061: 'Telerik.WebAii.Controls.Html.RadTextBox' does not contain a definition for 'Text' and no extension method 'Text' accepting a first argument of type 'Telerik.WebAii.Controls.Html.RadTextBox' could be found (are you missing a using directive or an assembly reference?)
18:27:31 'INFO' > Build Failed

codedstep code:

using Telerik.TestStudio.Translators.Common;
using Telerik.TestingFramework.Controls.TelerikUI.Blazor;
using Telerik.TestingFramework.Controls.KendoUI.Angular;
using Telerik.TestingFramework.Controls.KendoUI;
using Telerik.WebAii.Controls.Html;
using Telerik.WebAii.Controls.Xaml;
using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;

using ArtOfTest.Common.UnitTesting;
using ArtOfTest.WebAii.Core;
using ArtOfTest.WebAii.Controls.HtmlControls;
using ArtOfTest.WebAii.Controls.HtmlControls.HtmlAsserts;
using ArtOfTest.WebAii.Design;
using ArtOfTest.WebAii.Design.Execution;
using ArtOfTest.WebAii.ObjectModel;
using ArtOfTest.WebAii.Silverlight;
using ArtOfTest.WebAii.Silverlight.UI;

namespace TestProject4
{

    public class WebTest : BaseWebAiiTest
    {
        #region [ Dynamic Pages Reference ]

        private Pages _pages;

        /// <summary>
        /// Gets the Pages object that has references
        /// to all the elements, frames or regions
        /// in this project.
        /// </summary>
        public Pages Pages
        {
            get
            {
                if (_pages == null)
                {
                    _pages = new Pages(Manager.Current);
                }
                return _pages;
            }
        }

        #endregion
        
        // Add your test methods here...
    
        [CodedStep(@"New Coded Step")]
        private void CompleteWithZeros(RadTextBox textbox, int length)
 {
     var text = CompleteWithZeros(textbox.Text, length);
     textbox.Text = text;
 }
            
        }
    
}