Answer
$p = 440$ vibrations per second.
Work Step by Step
Since the pitch varies INVERSELY with the wavelength, we can express it as such:
$$pw=k$$
where $p$ is the pitch, $w$ is the wavelength and $k$ is the proportionality constant. Since we know that, when $p=660$, $w=1.6$, we can calculate $k$:
$$k=pw=(660)(1.6)=1056$$
and now answer the question:
$$1,056=p(2.4)$$
$$\frac{1,056}{2.4} = p$$
$$440 = p$$