what is meant by the code. please explain the code?

<pre lang="cs">public class Activity {
    private string id;
    private string description;
    private int duration;
    private int est;
    private int lst;
    private int eet;
    private int let;
    private Activity[] successors;
    private Activity[] predecessors;
}
///////////////////////////////////////////////////
private static Activity[] WalkListAback(Activity[] list)
    {
        list[na - 1].Let = list[na - 1].Eet;
        list[na - 1].Lst = list[na - 1].Let - list[na - 1].Duration;

        for(int i = na - 2; i &gt;= 0; i--)
        {
            foreach(Activity activity in list[i].Successors)
            {
              if(list[i].Let == 0)
                list[i].Let = activity.Lst;
              else
                if(list[i].Let &gt; activity.Lst)
                  list[i].Let = activity.Lst;
            }

            list[i].Lst = list[i].Let - list[i].Duration;
        }
        return list;
    }
</pre>