Answer
$\Phi = 1.82~eV$
Work Step by Step
We can find the work function:
$hf = K_{max}+\Phi$
$\frac{hc}{\lambda} = K_{max}+\Phi$
$\Phi = \frac{hc}{\lambda} - K_{max}$
$\Phi = \frac{(6.63\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}{491\times 10^{-9}~m} - 0.710~eV$
$\Phi = 4.0509\times 10^{-19}~J-0.710~eV$
$\Phi = (4.0509\times 10^{-19}~J)(\frac{1~eV}{1.6\times 10^{-19}~J})-0.710~eV$
$\Phi = 1.82~eV$
