\(\,{\lambda _{\text{0}}}\, = \,\,\,\frac{{hc}}{{{\phi _0}}}\,\left( {\because \,\,{\phi _0}\,\, = \,\,h{{f}_0}\, = \,\,\frac{{hc}}{{{\lambda _0}}}} \right)\,\,\)
\( = \,\,\,\frac{{6.6\,\, \times \,\,{{10}^{ - 34}} \times \,\,3\,\, \times \,\,{{10}^8}}}{{1.6\,\, \times \,\,1.6\,\, \times \,\,{{10}^{ - 19}}}}\,\,\, = \,\,7.734\,\, \times \,\,{10^{ - 7}}m\,\, = \,\,7734\)