Answer
Please see the work below.
Work Step by Step
We know that
$v=\frac{d}{t}$
We plug in the known values to obtain:
$v=\frac{1250000}{307.2}=4069\frac{m}{s}$
We also know that
$v=\lambda f$
This can be rearranged as:
$\lambda=\frac{v}{f}$
We plug in the known values to obtain:
$\lambda=\frac{4069}{3.21}=1267.6m$
