Photoelectric Effect Wave Theory Light

A certain metallic surface is illuminated by monochromatic radiation of wavelength $\lambda .$  The stopping potential for photoelectric current for this radiation is 3V₀. If the same surface is illuminated with a radiation of wavelength $2\lambda ,$  the stopping potential is V₀. The threshold wavelength of this surface for photoelectric effect is_________   $\lambda .$

A beam of electromagnetic radiation of intensity $6.4*{10}^{-5}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$  is comprised of wavelength, $\lambda =310\mathrm{n}\mathrm{m}$ . It falls normally on a metal (work function $\phi =2\mathrm{e}\mathrm{V}$  ) of surface area $1{\mathrm{c}\mathrm{m}}^2$ . If one in ${10}^3$  photons ejects an electron, total number of electrons ejected in is ${10}^x.\left(h_c=1240\mathrm{e}\mathrm{V}\mathrm{n}\mathrm{m},1\mathrm{e}\mathrm{V}=1.6*{10}^{-19}\mathrm{J}\right)$ , then $\mathrm{x}$  is