c# - Visual Studio のエラー: 型 'string' を 'int' に暗黙的に変換できません

Question

これは宿題です。C# を使用した Visual Studio の ASP.NET MVC アプリです。実行すると、次の行を参照して、「タイプ 'string' を 'int' に暗黙的に変換できません」というエラーが表示されます: Manufacturer = collection["Manufacturer"], Gears = collection["Gears"], Frame = collection[ "Frame"] と Gears = collection["Gears"] の下に波線があります。

using MvcApplication3.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace MvcApplication3.Controllers
{
    public class BikeController : Controller
    {
        //
        // GET: /Bike/

        List<Bike> bikes;


        public BikeController()
        {
            if (bikes == null)
            {
                bikes = new List<Bike> {
                new Bike(),
                new Bike { Manufacturer = "Nishiki", Gears = 5, Frame = "Road" }
            };
            }
        }

        public ActionResult Index()
        {
            return View(this.bikes);
        }

        private ActionResult View(Func<object> func)
        {
            throw new NotImplementedException();
        }

        //
        // GET: /Bike/Details/5

        public ActionResult Details(int id)
        {
            var currentBikes = bikes[id];
            return View(currentBikes);

        }

        //
        // GET: /Bike/Create

        public ActionResult Create()
        {
            return View();
        }

        //
        // POST: /Bike/Create

        [HttpPost]
        public ActionResult Create(FormCollection collection)
        {   
            Bike b = new Bike
            { 
                Manufacturer = collection["Manufacturer"], Gears = collection["Gears"], Frame = collection["Frame"]
            };
            bikes.Add(b);
            try
            {
                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

        //
        // GET: /Bike/Edit/5

        public ActionResult Edit(int id)
        {
            return View(bikes.Where(b => b.BikeID == id).First());
        }

        //
        // POST: /Bike/Edit/5

        [HttpPost]
        public ActionResult Edit(int id, FormCollection collection)
        {
            try
            {
                // TODO: Add update logic here

                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

        //
        // GET: /Bike/Delete/5

        public ActionResult Delete(int id)
        {
            return View();
        }

        //
        // POST: /Bike/Delete/5

        [HttpPost]
        public ActionResult Delete(int id, FormCollection collection)
        {
            try
            {
                // TODO: Add delete logic here

                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

        public int bike { get; set; }
    }
}