C# class definition HELP
<p>This is a project question that i just cant seem to answer</p>

<pre><code>using System;

namespace ConsoleApplication2
{
    internal class Equipment : IComparable
    {
        private readonly string type;
        private readonly int serialNo;
        private string colour;
        public decimal cost;

        public Equipment(string type, int serialNo)
        {
            this.type = type == null ? "" : type.Trim();
            this.serialNo = serialNo;
        }

        public string Key
        {
            get { return type + ":" + serialNo; }
        }

        int IComparable.CompareTo(object obj)
        {
            return 0;
        }
    }
}
</code></pre>

<p>(a) Override the appropriate method o ensure that different instances of the class that represent the same equipment item will be considered the same in the system.</p>

<p>(b) Override the appropriate method to enable instances of this class to be stored (and found) by key in a hash table</p>
