What does it mean for a line to have an undefined slope?

Country carpets charges $22 per square yard for carpeting, and an additional installation fee of $100. city carpets charges $25 per square yard for the same carpeting, and an additional installation fee of $70

Which best explains why this triangle is or is not a right triangle?

Which inequality comparing two of the expressions is true when 0.7 < x < 0.9