Ca is excited by light of 422.7nm. What is the energy difference between ground and excited states?

Question

I have the answer from the back of the book, what I am looking for is the appropriate eqn., so I can do the problem on my own in the future. Thanks:)

Answer 1

The energy of the photon is h*c/L, where h = Planck's constant, c = velocity of light..

h = 6.63*10^-34 joule sec

c = 3*10^8 m/sec