並ぶ is when something is lining up. 並べる is when you're lining something up. You know this because when it comes to bears (べる), you have to line them up yourself, because they won't be doing it for you, that's for sure.
The reading can come from 並ぶ, so if you know that you can figure out the reading for this one as well.
Why did it take you so long to set up the bowling pins?