Answer
Since the required speed is faster than the speed of light, it is not possible that one event caused the other event.
Work Step by Step
We can calculate the required speed for information to travel to allow one of the events to cause the other event:
$v_{req} =\frac{\Delta x}{\Delta t} = \frac{400~m}{1.00\times 10^{-6}~s} = 4.0\times 10^8~m/s$
Since the required speed is faster than the speed of light, it is not possible that one event caused the other event.
