Add project files.

Helpers/ComboboxItem.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Helpers
+{
+    public class ComboboxItem
+    {
+        private readonly string _display;
+        private readonly int _hidden;
+
+        public ComboboxItem(string display,int hidden)
+        {
+            _display = display;
+            _hidden = hidden;
+        }
+        public int HiddenValue
+        {
+            get
+            {
+                return _hidden;
+            }
+        }
+
+        public override string ToString()
+        {
+            return _display;
+        }
+    }
+}

Helpers/Helpers.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>

Helpers/StringExtensions.cs

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+using System;
+using System.Globalization;
+
+namespace Helpers
+{
+    public static class StringExtensions
+    {
+        public static bool IsNumeric(this string s)
+        {
+            return float.TryParse(s, NumberStyles.Float | NumberStyles.Integer, CultureInfo.CurrentUICulture, out _);
+        }
+    }
+}