3.00*10^8 m/s / 590nm
First convert the nanometres to metres: 590nm = 590*10^-9 m = 5.9*10^-7
frequency = 3*10^8/(5.9*10^-7) = (3/5.9)*10^15 = 0.508*10^15 = 5.08*10^14 sec^-1
