A particle undergoes SHM with a time period of 2 seconds in how much time will it travel from its mean position to a displacement equal to half of its amplitudea-0.5 secb-1/3secc-1/4secd-1/6secAnd why is omega t =π/6?

A simple pendulum whose length is slightly less than that of a seconds pendulum start vibrating with another seconds pendulum in the same phase. After 18 seconds, they again vibrate in the same phase. The periodic time of simple pendulum is-