As simple as the 'S' of SHM

The average speed over the period of complete oscillation of a particle performing rectilinear simple harmonic motion is $2\text{ cm s}^{-1}$ . If the particle attains this speed when it is at a point $P$ whose distance from the equilibrium position $O$ is $4 \text{ cm}$ , then find the time period (in seconds) of the complete oscillation (rounded to two places of decimal).