What exactly is your problem?
It is unclear from your post what it is you want...
You have just posted a question plus its answer,
what reply are you expecting?
There are well defined mathematical methods for defining the interaction between wavelength and diffraction grating.
If you are being asked these questions then it must be assumed that you should know these mathematical equations
(or at least know where to find them)
Given these mathematical equations, the answers should be just a matter of plugging the appropriate values into the appropriate places in the equations.
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