How to calculate the frequency given a colour, angle, 100 slits/mm.

[Ninja_Truth]

So for my assignment I have to calculate the wavelength given an angle, colour, 100 slits/mm diffraction rating but no frequency.
Angle = 3.4 degrees
Colour = Purple

For v =∫λ,
I need the wavelength or frequency to work out anything, v is the speed of light. But I cannot see how to find this without the frequency and I need a wavelength to work out the frequency.

Can anyone help?

 

[BOAS]

Do you have a textbook that covers diffraction gratings, or the double slit experiment? The condition for the maximums is actually the same in both cases.

From this equation you will be able to find λ