29. You wish to resolve the calcium-H line at 396.85 nm from the hydrogen- line at 397.05 nm in a first-order spectrum. To the nearest hundred, how many lines should your grating have? 26. (a) Find the resolving power of a grating needed to separate the sodium-D spectral lines, which are at 589.0 nm and 589.6 nm. (b) How many lines must the grating have to achieve this resolution in first order?