The correct answer is 129 days option b
Explaination :
BY keplers third law \(T^2 \propto R^3\)
\(\therefore { ({ T_2\over T_1})^2=({ R_2\over R_1})^3}\)
T_{1 }= 365 days , R_{1} =R , R_{2} = R/2
\({ ({ T_2\over 365})^2=({{ R_2/2}\over R_1})^3}\)
\(T_2^2={(365)^2\over8}\)
\(T_2^2=16653
\) ----{note: \(129^2=16641 \) but 16653 is nearby 129 hence due to option answer is 129}
\(T_2=129 \space days\)