Relations between different time complexities of an algorithm
Let us use the following notations:


$L$ is any lower bound on the running time.
$U$ is any upper bound on the running time.
$B$ is the best case running time.
$W$ is the worst case running time.
$A$ is the average case running time.


These parameters are related in the following way:

$$ L \leq B \leq A \leq W \leq U. $$

You can solve the question using these relations.

Make sure that you understand why they hold.