Sound waves travel at $350$ m/s through a warm air and at $3500$ m/s through brass. Which of the following is correct about the wavelength of a $700$ Hz accoustic wave as it enters brass from warm air?

The distance between two consecutive points with phase difference of $60^\circ$ in a wave of frequency $n$ is $x$ meter. The velocity with which wave is traveling is

A traveling wave is described by the equation $y(x, t) = [0.05 \sin (8x - 4t)]$ m
The velocity of the wave is [All the quantities are in SI unit]

The electric potential at the center of two concentric half rings of radii $R_1$ and $R_2$, having same linear charge density $\lambda$ is ($\epsilon_0$ = permittivity of free space)