Answer
Since the required speed is greater than $c$, the events can not be causally related.
Work Step by Step
Event 2: The rear door reaches the front bumper at $t_{c2} = -1.01\times 10^{-7}~s$
Note that $x_{c2} = 30.5~m$
Event 1: The front door reaches the rear bumper at $t_{c1} = 0$, which is after the rear door reached the front bumper.
Note that $x_{c1} = 0$
We can find the speed required for information from event 2 to reach event 1:
$v = \frac{\Delta x}{\Delta t}$
$v = \frac{30.5~m}{1.01\times 10^{-7}~s}$
$v = 3.02\times 10^8~m/s$
Since the required speed is greater than $c$, the events can not be causally related.
