Answer
The minimum energy needed to eject an electron is $7.222\times10^{-19}J$.
Work Step by Step
*Strategy:
The minimum energy needed to eject an electron is the energy of a photon of radiation with a minimum frequency of $1.09\times10^{15}s^{-1}$ which can be acquired by this formula: $$E_{min}=h\times\nu_{min}$$
$E_{min}$ : minimum energy of a photon of radiation needed to eject an electron off its surface
$h$ : Planck's constant ($h\approx6.626\times10^{-34}J.s$)
$\nu_{min}$ : minimum frequency of radiation needed to eject an electron off its surface ($\nu_{min}=1.09\times10^{15}s^{-1})$
Therefore, the minimum energy needed to eject an electron is:
$E_{min}=h\times\nu_{min}=(6.626\times10^{-34})\times(1.09\times10^{15})\approx7.222\times10^{-19}J$
