Answer:
Two lines only can intercept if they have different slopes, if they have the same slope, the lines are parallel and they never intercept.
So if the cost of producing a book is different than the price of selling the book, the lines will intercept at some point.
Where the equations can be:
lose = A*x + b
win = C*x + d
where x is the number of books, A and C are the slopes, b and d are constants. Those two lines only will intercept if A is bigger than C, the intercept will be for x different than zero only when b is different than d
