A student uses a diffraction grating to determine the wavelength of visible light from a source. The diffraction grating has 300 lines per mm. The student measures the angle θ of each order n of the intensity maxima. A graph of n against sin θ is plotted. The line of best fit for the plotted points is shown and has gradient G. [Diagram shows a graph of n (y-axis) against sin θ (x-axis), a straight line passing through the origin with positive gradient G.] Which expression represents the wavelength, in m, of the visible light in terms of G?