3X-9Y= 9, 3Y=X +12, 2X- 6Y= 12
Basic Rule: slopes equal means lines parallel (unless the two lines are the same); slopes which are negative reciprocal of each other are perpendicular.
Slopes of your lines in order given:
1/3, 1/3, and 1/3
.
(Are any pair of your lines the same line?)