Structure of Atom · Photoelectric effect

The surface of sodium metal is irradiated with radiation of wavelength x nm. The kinetic energy of ejected electrons is $2.8\times10^{-20}$ J. The work function of sodium is 2.3 eV. The value of x is $\times10^{2}$ nm. (Nearest integer)

(Given : $h = 6.6\times10^{-34}$ J s; 1eV $= 1.60\times10^{-19}$ J; $c = 3.0\times10^{8}$ m s$^{-1}$)