In Young's double-slit experiment, the slits are separated by 0.28 mm, and the screen is placed 1.4 m away. The distance between the central bright fringe and the fourth bright fringe is measured to be 12 cm. Then, the wavelength of light used in the experiment is …….
What comes next in the series?
\(2, 6, 12, 20, 30, \ ?\)