The diesel goes 45 km/h so in 4 hours will have gone 4(45)= 180 km. Since it started 14 hours after the cattle train, 4 hours after the diesel started will be 14+ 4= 18 hours after the cattle train started. If we let v be the average speed of the cattle train, in km/h, in 18 hours, it will have gone 18v km. Since the diesel caught up to it then, they have gone the same distance: 18v= 180 so v= ?