The person himself reach the city E from coast A , by travelling through B, C and D each at 30 km} each in 4 days. Then, when returning he will spend his rations at D , where he will be joined by second person with ration of 2 days. At C , third person will be there with ration of 3 persons for one day. Again at B , fourth person will be there, with ration of 4 persons for one day, and hence finally all 4 will reach the coast A .