A metal surface is illuminated by light of two different wavelengths 248 nm and 310 nm . The maximum speeds of the photoelectrons corresponding to these wavelengths are $u_1$ and $u_2$, respectively. If the ratio $u_1: u_2=2: 1$ and $\mathrm{hc}=1240 \mathrm{eV} \mathrm{nm}$, the work function of the metal is nearly