The question in hand is a typical word-play problem.

The argument suggests that citizens of Parktown are worried about "SERIOUS CRIMES" and later the argument concludes keeping local teenagers won't affect the concerns of citizens as "MOST CRIMES" are committed by teenagers take place between 3pm to 6pm.

Now you can see the word-play and therefore the flaw in the argument.

[A] is irrelevant

it says crimes in the afternoon are small theft and vandalism. This leaves open the possibility that SERIOUS CRIME will occur after afternoon.

[C] again the possibility of Serious Crime in evening exists

[D] is out of scope.

[E] invalid as weekend will be vulnerable for citizens