In order to plot point (2, 8), we move 2 cm along x-axis and 8 cm along y-axis. The point we arrive at is (2, 8).
To plot point (7, 8), we move 7 cm along x-axis and 8 cm along y-axis. The point we arrive at is (7, 8).
To plot point (12, 8), we move 12 cm along x-axis and 8 cm along y-axis. The point we arrive at is (12,8).

After plotting points, we observe that all points are having same ordinate ( ie. same y-coordinate.)

Hence, all points lie on the same line.