This article has a great video that explains the process of PBL or in this case CBL. Note to Laurie-I am not sure that the original challenge is correct because there isn't a clear call to action.
The learners identify lessons, simulations, activities, and content resources, to answer the guiding questions and set the foundation for them to develop innovative, insightful, and realistic solutions.
Challenge Based Learning is collaborative and hands-on
By design, the big idea allows for the generation of a wide variety of essential questions that reflect the interests of the students and the needs of their community.
From the essential question a concise challenge is articulated that asks the learners to create a specific solution that will result in concrete, meaningful action.