A monochromatic laser beam is directed normally at an adjustable single slit of width \(a\).

The resulting diffraction pattern is projected onto a flat screen positioned a fixed distance \(L\) from the slit, where \(L \gg a\).

A student measures the total width \(W\) of the central bright maximum (the distance between the first intensity minima on either side of the center) for several different values of \(a\).

Which of the following identifies the quantities that should be plotted on the vertical and horizontal axes to produce a linear graph, and the correct relationship to calculate the wavelength \(\lambda\) of the laser from the slope \(S\) of the line of best fit?