In the figure, sound waves $\backslash ($ A $\backslash )$ and $\backslash ($ B $\backslash ),$ both of wavelength $\backslash (\backslash$lambda $\backslash ),$ are initially in phase and traveling rightward, as indicated by the two rays. Wave $\backslash ($ A $\backslash )$ is reflected from four surfaces but ends up traveling in its original direction. Wave $\backslash ($ B $\backslash )$ ends in that direction after reflecting from two surfaces. Let distance $\backslash ($ L $\backslash )$ in the figure be expressed as a multiple $\backslash ($ q $\backslash )$ of $\backslash (\backslash$lambda: L$=$q $\backslash$lambda $\backslash ).$ What are the $($a$)$ smallest and $($b$)$ second smallest values of $\backslash ($ q $\backslash )$ that put $\backslash ($ A $\backslash )$ and $\backslash ($ B $\backslash )$ exactly out of phase with each other after the reflections?

$($a$)$ Number

Unit

$($b$)$ Number

Unit