Hello MOOC Team,
Thank you for the excellent MOOC.
Above is classified as lecture but it seems like an exercise. Also, where can find the solution for that exercise?
Yes, we changed a bit the structure for this module. We start with an introductory exercise for each subsection and the correction is given in the next lecture.
You are not the first person to report that this structure is surprising. We will change it for the next version of the MOOC 
Hum I understand better, exercises are still before lecture