Answer
We can rank the shuttle craft according to the frequency we receive:
$(b) \gt (a) \gt (c) \gt (d)$
Work Step by Step
We can write an expression for the received frequency when a source is moving away from us with a speed $v$:
$f = f_0~\sqrt{\frac{1-v/c}{1+v/c}}$
We can see that $f \lt f_0$ and the received frequency $f$ decreases as $v$ increases.
We can write an expression for the received frequency when a source is moving toward us with a speed $v$:
$f = f_0~\sqrt{\frac{1+v/c}{1-v/c}}$
We can see that $f \gt f_0$ and the received frequency $f$ increases as $v$ increases.
We can rank the shuttle craft according to the frequency we receive:
$(b) \gt (a) \gt (c) \gt (d)$
