Problem regarding inheritance

Question

Write a program to define a class College BUS and a class BusEngine .Let the CollegeBus class contain BusEngine .The BusEngine should be started at the College Campus and stopped after reaching the destination (say Y ) .Let the speed and the distance be read.The Program should throw an exception when the CollegeBus tries to travel beyond destination or speed increase beyond 100 kmper hour. Develop the application in C#.

i am not understanding my mistake

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


public class CollegeBus
{
    public static int speed;
    public static float distance;
    public CollegeBus(int s, float d)
    {
        speed = s;
        distance = d;
    }
}

public class Engine : CollegeBus
{
    string str1;
    string str2;
    public Engine(string s1, string s2)
        : base(speed, distance)
    {
        str1 = s1;
        str2 = s2;
        Console.WriteLine("Source is {0} and destination is {0}",s1,s2);
        if (distance > 30)
            throw new DistanceExceededException();
        if (speed > 100)
            throw new SpeedExceededException();
    }
}

class Travel
{
    public static void Main()
    {
        CollegeBus b=new CollegeBus(40,20);
        //Engine e=new Engine("X","Y");
        b.Engine.str1=40;
        b.Engine.str2=20;
    }