A sound wave of frequency $f$ travels horizontally to the right. It is reflected from a large vertical plane surface moving to the left with a speed $v$. The speed of sound in the medium is $c$, then

the frequency of the reflected wave is $\frac{f\left(c+v\right)}{c-v}$

the wavelength of the reflected wave is $\frac{c\left(c-v\right)}{f\left(c+v\right)}$

the number of waves striking the surface per second is $\frac{f\left(c+v\right)}{c}$

the number of beats heard by a stationary listener to the left of the reflecting surface is $\frac{fv}{c-v}$