From the question, we were made to understand that Rosenburg, which is indicated as point R on the map, is the mid-point of Springfield to Junction city. Thus, the number of miles at Rosenburg, point R will be given by:

If 55 miles have already been travelled, the distance to be covered to stop for lunch at Rosenburg, point R will be: 180 - 55 = 125 miles
Hence, how much farther that must be travelled before they stop for lunch is 125 miles, which is Option D.