Correct Answer - B
Let spring constant of each spring be k then the equivalent spring constant of the two spring system in parallel is 2k
Without mass, `T=3s=2pisqrt((12)/(2k))`
With mass, `T_1=65=2pisqrt((12+m)/(2k))`
`(T)/(T_1)=(1)/(2)=sqrt((12)/(12+m))`
`m=36kg`