A sinusoidal wave travelling in the positive x-direction has an amplitude of `15.0 cm`, a wavelength of `40.0 cm` and a frequency of `8.00 Hz. The verticle displacement of the medium at `t = 0 and x = 0` is also `15.0 cm` as shown in figure.

(a) Find the angular wave number `k`, period `T`, angular frequency `omega` and speed `v` of the wave.
(b) Write a general expression for wave function.