Answer
$\frac{1}{210}$
Work Step by Step
We know that $probability=\frac{\text{number of favorable outcomes}}{\text{number of all outcomes}}$
The number of all outcomes is $7!$, out of these $4!$ correspond to the desirable selection (because out of the seven films $4$ have their places in the order fixed)
Hence here the probability is $\frac{4!}{7!}=\frac{1}{210}$
