Dual Nature of Radiation

A Hydrogen-like atom has atomic number Z. Photons emitted in the electronic transitions from level n=4 to level n=3 in these atoms are used to perform photoelectric effect experiment on a target metal. The maximum kinetic energy of the photoelectrons generated is 1.95‌eV. If the photoelectric threshold wavelength for the target metal is 310‌nm, the value of Z is____________
[Given hc=1240‌eV-nm and Rhc=13.6‌eV, where R is the Rydberg constant, h is the Planck's constant and c is the speed of light in vacuum]