Silver $($Ag$)$ and lithium $($Li$)$ metals have work functions$()$

$$ of $4\mathrm{.}74$ and $2\mathrm{.}9$ eV$,$ respectively.

What is the threshold wavelength $($or frequency$)?$ Which metal is a better photocathode $($i$.$e$.,$ which has a lower

threshold frequency$)?($Note: hc $=1240$ eV nm or assume a $1$ V electric field