You might want to go to this website, http://www.indiana.edu/~p1013447/dictionary/mendel.htm
Welcome, And i hope this helps :P
The object<span> is moving with a decreasing acceleration. The </span>object<span> is moving with </span>a constant<span> velocity.</span>
To solve this problem we will apply the concepts related to wavelength as the rate of change of the speed of the wave over the frequency. Mathematically this is

Here,
v = Wave velocity
f = Frequency,
Replacing with our values we have that,

\lambda = 0.68m
The distance to move one speaker is half this

Therefore the minimum distance will be 0.34m
A and C Im pretty sure :)