Answer:
0.4 Hz
Step-by-step explanation:
For an object in simple harmonic motion, the relationship between frequency and period is:

where:
f is the frequency (the number of complete oscillations per second)
T is the period (the time it takes for the object to complete one oscillation)
In this problem, we have an object with a period of oscillation of
T = 2.5 s
Therefore, the frequency of oscillation is:

Here we also want to know the direction of the restoring force. A simple harmonic motion is a motion in which there is a restoring force proportional to the displacement:

where
k is the spring constant
x is the displacement
We notice in the formula that there is a negative sign: it means that the direction of the force is opposite to the displacement. Therefore, the force always points towards the equilibrium position of the system.