138 A spectroscope is used with a diffraction grating that has 4000 slits/cm. On the screen where the diffraction pattern is formed, the distance between the yellow (with a wavelength of 520 nm) and violet (with a wavelength of 400 nm) lines of the second light band is 20.0 cm. What is the distance between the screen and the reticle? What color is the fringe closest to the central high? [1.67m]