Simple Harmonic Motion

The position, velocity and acceleration of a particle executing simple harmonic motion are found to have magnitudes of \(4 \mathrm{~m}, 2 \mathrm{~ms}^{-1}\) and \(16 \mathrm{~ms}^{-2}\) at a certain instant. The amplitude of the motion is \(\sqrt{x}, \mathrm{~m}\) where \(x\) is _________.