c
\({\rm{2K}} = \frac{{{\rm{hc}}}}{{{\rm{310}}}} - h{v_0}\,\,\,\,\,\,......(1)\)

\(\,K = \frac{{hc}}{{400}} - h{v_0}\,\,\,\,\,\,\,.....(2)\,\)

\(2 \times 2 \Rightarrow 2K = \frac{{2hc}}{{400}} - 2h{v_0}\,\,\,\,\,\,\,.....(3)\)

\((3) - (2)\) \( \Rightarrow 0 = \frac{{2hc}}{{400}} - 2h{v_0} - \frac{{hc}}{{310}} + h{v_0}\)

\( \Rightarrow \,h{v_0} = hc\left[ {\frac{{110}}{{310 \times 200}}} \right]\,\,\,\)

\( \Rightarrow \,\,\,h{v_0} = \frac{{1240 \times 110}}{{310 \times 200}}eV = 2.2\ eV\)