This question has to do with slope. If two lines share the same slope but different points, then there are parallel. If their slopes are negative reciprocals (like -2 and 1/2), then they are perpendicular.
y = 3x - 7 and y = 3x + 1 have different points but both have a slope of 3, where y = mx+b,
m = slope. Therefore these two lines are parallel.