v=E/h
v is the frequency
h is the planks constant which is 6.626 x10^-34
v is therefore [2.668 x 10^-19] /6.626 x10^-34=4.027 x10^14
c(speed of light)=wavelength x frequency
c is always =3.0 x10^8
therefore wavelength = ( 3.08 x10^8)/4.027 x 10^14=7.649 x10^-7
convert to nm
=(7.649 x10^-7) x(1.0 x 10 ^9 nm)=764nm
