Not really sure if they have solutions listed somewhere. But the files including pbix solutions are available here
https://github.com/MicrosoftLearning/DA-100-Analyzing-Data-with-Power-BI
Probably, you can post a question on Power BI forum and someone can provide the answers there
https://community.powerbi.com/t5/Forums/ct-p/PBI_Comm_Forums
Please don't forget to Accept Answer and Up-vote if the response helped -- Vaibhav