A sinusoidal sound wave moves through a medium and is described by the displacement wave function

s(x, t) = 2.00 cos (15.7x - 858t)

where s is in micrometers, x is in meters, and t is in seconds.
determine the instantaneous displacement from equilibrium of the elements of the medium at the position x = 0.050 7 m at t = 3.08 ms.