What is the phase difference between consecutive crest and trough?

The number of waves contained in unit length of the medium is called

The equation of a longitudinal wave is represented as $y = 20 \cos \pi (50t - x)$. Its wavelength is ..... $cm$.

You have learnt that a travelling wave in one dimension is represented by a function $y=f(x, t)$ where $x$ and $t$ must appear in the combination $x-vt$ or $x+vt$,i.e.,$y=f(x \pm vt)$. Is the converse true? Examine if the following functions for $y$ can possibly represent a travelling wave:
$(a)$ $(x-vt)^2$
$(b)$ $\log[(x+vt)/x_0]$
$(c)$ $1/(x+vt)$

Two waves are represented as $y_1 = a_1 \sin \left( \omega t - \frac{2\pi x}{\lambda} \right)$ and $y_2 = a_2 \cos \left( \omega t - \frac{2\pi x}{\lambda} + \frac{\pi}{6} \right)$. The path difference between the two waves is:

$A$ wave equation is given by $y = 10^{-4} \sin(60t + 2x)$,where $x$ and $y$ are in $meters$ and $t$ is in $seconds$. Which of the following statements is correct?