The work function of a metal surface is 4.80 10-19J. The maximum speed of the electrons

Question:

The work function of a metal surface is 4.80 × 10-19J. The maximum speed of the electrons emitted from the surface is vA = 7.30 × 105 m/s when the wavelength of the light is λA. However, a maximum speed of vB = 5.00 × 105 m/s is observed when the wavelength is λB. Find the wavelengths λA and λB.