Structure of Atom Part 1

What is the work function of the metal if the light of wavelength 4000 Å generates photoelectrons of velocity 6 × 105 ms–1 form it ?
(Mass of electron = 9 × 10–31 kg
Velocity of light = 3 × 108 ms–1
Planck's constant = 6.626 × 10–34 Js
Charge of electron= 1.6 × 10–19 JeV–1)