When sodium metal is illuminated by light of wavelength 4.2*10^2 nm, the stopping potential is found to be 0.655 Volt. when the wavelength is changed to 3.1*10^2nm, the stopping potntial is 1.69 Volt. Using only these data and the values of speed of light c and electronic charge e, find the work function of sodium, and a value for Planck's constant.