The question has already been answered however one very simple way to approach the problem is as follows:
What is happening in the question is that there are reports of accidents occurring per day, which means that for one accident to occur, chances are $1\over7$.
Now if an accident has occurred then we want the remaining $6$ accidents to occur on the same day. Since each accident has a probability of $1\over7$, therefore for $6$ consecutive accidents it will be $\left(1\over7^6\right)$ which is option number B