Answer
(a) increase
(b) $0.360m$
Work Step by Step
(a) We know that frequency and wavelength are inversely proportional. Thus, if the frequency of the speakers is lowered then the required distance will increase.
(b) The required distance can be calculated as
$d=\frac{\lambda}{4}$
$\implies d=\frac{v}{4f}$
We plug in the known values to obtain:
$d=\frac{343}{4(238)}=0.360m$
