A student holds a tuning fork oscillating at $256$ Hz$.$ He walks toward a wall at a constant speed of $1\mathrm{.}55$ m$/$s$.$

$($a$)$ What beat frequency does he observe between the tuning fork and its echo?

Hz

$($b$)$ How fast must he walk away from the wall to observe a beat frequency of $5\mathrm{.}10$ Hz$?$

m$/$s