From the graphs shown in the attached file we can see that the maximum number of shoes bought were of size 9. On both days the number of size 9 shoes bought was 5 which was the highest number of shoes bought for any size shoe. Therefore since size 9 sell the most on both days the owner should stock most of size 9 shoes in the store's inventory.
Since the second line is parallel to the first, it will have the same slope. The y-intercept of the new line is 4 (because of the coordinates given) so the equation of Lynda's second cut is y = 1/4x + 4 which is choice C