a beam of blue light has a wavelength of 595 nm. What is the frequency

Since this is not my area of expertise, I searched Google under the key words " wavelength frequency" to get these possible sources:

http://zebu.uoregon.edu/~soper/Light/frequency.html
http://www.sengpielaudio.com/calculator-wavelength.htm
http://www.1728.com/freqwave.htm
http://ceres.hsc.edu/homepages/classes/astronomy/fall97/Mathematics/sec12.html
(Broken Link Removed)

In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.

I hope this helps. Thanks for asking.