Question

Every 6 seconds a pendulum completes one cycle. 

Answer 1

The period is 2.4 seconds and the frequency is I believe 1/6 I'm not entirely sure since I don't think this question has enough information.

Answer 2

The period is the time it takes any repeating process
to complete one cycle.  You just told us what it is for the
pendulum . . . 6 seconds.

The frequency is the reciprocal of the period.  For the pendulum,
that's

                 1 / (6 sec) = (1/6) per second = 1/6 Hertz .