According to Einstein's photoelectric equation,

$K_{\max }=h\upsilon -{\varphi }_0$

where $K_{\max }$ is the maximum kinetic energy of photoelectrons and ${\varphi }_0$ is the work function of the metal surface

Initially,

$h\upsilon =0.4+{\varphi }_0$

When the frequency is increased by $40\%$, then

$1.4h\upsilon =1.2+{\varphi }_0$

On solving we get

${\varphi }_0=1.6 \mathrm{eV}$