I would suggest you to define scale factor.
You can choose the scale like this:
Along x - axis, 1 cm = 3 units and
along y-axis, 1 cm = 3 units
Also, it would be easier to graph, if you choose the combinations like this:
x = 3 and y = 12
x = 6 and y = 9
x = 9 and y = 6
So, the points on the graph would be (1, 4), (2, 3) and (3, 2).