What do merchants do?

In the homework section of Lingua Latina, chapter 10, is a question that causes trouble for many of my students.

The question, “Quid agunt mercatores” hinges on the verb “agunt”.   The verb, which means, to do, is fully conjugated here: http://latindictionary.wikidot.com/verb:agere

If you have also encountered this difficulty, the following video should help.