\({a_{Mn}} = \frac{{{a_c} + {a_m}}}{2}\)
\( = 1.89 \times {10^{11}}m\)
From kepler's law
\({T^2} \propto {R^3}\)
\(\therefore \,{\left( {\frac{{{T_{mn}}}}{{Te}}} \right)^2} = {\left( {\frac{{{R_M}}}{{{\operatorname{R} _e}}}} \right)^3}\)
\(\therefore {T_{Mn}} = 518\,days\)
\(\therefore \operatorname{Re} duired\,time\, = \frac{{518}}{2} = 260\,days\)