Aline segment is drawn from (1, 9) to (4, 9) on a coordinate grid.

which answer explains one way that the length of this line segment can be determined?

Firstly, This is what I think you know too. The numbers are always written like that (x,y). So, (1,9) and (4,9) , both of their y-axis are 9. Therefore, When a line is drawn, they intersect one another.

These are the multiples of 15 but what you are probably asking or what are the factors of 15