answer:
C: 400
explanation:
basically on the graph what you do is you find the first term in the two subject textbook title. so for physics - biology, you would go to the horizontal axis and find the physics section. then what you do is find the biology section on the vertical axis. find the square they intersect at. the number inside that square is the number of physics - biology books sold per month.
if you do the same thing for the history - chemistry books, you’ll find that 300 of those are sold per month.
the difference between 700 and 300 is 400, giving you option C as your answer.
