Thought will start from Challenge 1 to brush up on learnings(and also brag about the badges ;-) )
Attached is my response using a formula in generate rows, then union and summarize. Looking at the number of posts, I am sure this is done multiple ways.
Started with the weekly challenges a little late, but excited to kick start it. My solution is not the best, but I was able to complete it using four tools only and without join.