What you would do, is add up on how many people have is Non-Fiction books and Fiction books. Once you have that, subtract it. You should get an answer of 2.
I am pretty sure the answer is 2,520.
Parallel lines always have the same slope. In fact that is the definition of parallel lines :P (Technically they have the same slope and different y-intercepts, because parallel lines can never intersect...)
D
