Hello @Tibbie,
You’re Welcome.
I’m glad that I was able to assist you in your query and you found the explanation useful.
So, in this scenario, if you break or analyze the measure into small steps then you’ll observe that several concepts came into the picture and they were collaborated together to achieve the final results.
So if you’ve gone through the “Mastering DAX Calculations” course, it’ll further strengthen your understanding of individual DAX functions and then you can integrate them to achieve the results like this.
Also, to fix the totals, one of our expert @Greg had already created a post where he has showcased various scenarios about how to fix them but this type of scenario was witnessed for the first time onto our forum. For understanding purposes, you can go through that post which you’ll find really helpful for future references. Below is the link of that post provided for reference.
Hoping you’ll find this helpful. 
Note: In order to view the entire post, please click onto the link and not onto the “expand/collapse” button.
Thanks and Warm Regards,
Harsh