When yellow sodium light, $=589$nm$=589$nm$,$ falls on a diffraction grating, its first$-$order peak on a screen $61\mathrm{.}0$ cmcm away falls $3\mathrm{.}19$ cmcm from the central peak. Another source produces a line $3\mathrm{.}86$ cmcm from the central peak. What is its wavelength? How many lines$/$cmlines$/$cm are on the grating?