Understanding a math problem

Solution 1:

I am unable to see how the houses are arranged.

The question is about "nineteen houses on the east side of Elm Street".

With no other information available, I would assume that Elm Street is a straight path in the north-south direction.

Presumably the nineteen houses on its east side are arranged in a row, each one having a portion of its property bordered by the street.

Other arrangements are possible (perhaps there is a cul de sac on which a few houses are located but their postal addresses are still officially on Elm Street, for example). But if you needed to consider such possibilities the special arrangement would have been mentioned in the problem statement.

Here's a Google Maps view of Elm Street in my city:

The lots I circled are the ones I would say are on the "east side" of the street, despite our Elm Street not running directly north-south.

Since no cross-streets were mentioned in your problem description you can either assume there are no cross streets, or that cross streets are ignored for the purpose of determining which homes are adjacent (i.e. two houses can be considered adjacent even if there is a cross street between them).