Help calculating inventory coverage

Hello, 

I work for a retailer and am building a dashboard to help model inventory coverage based on our inventory and sales. I am using power query/ power pivot but I'm not too familiar with DAX functions so I was hoping I could get some help here. 

The basic calculation I would like to do is for inventory coverage that I can bring into a pivot table. We calculate inventory coverage as: inventory/(sales for last 4 weeks/4). 

here is a link for a sample data set of what I am using showing the sales and inventory of the stores and warehouse: 

https://amersportsonline-my.sharepoint.com/:x:/g/personal/ardi_sardashti_amersports_com/EeSjobC4xgZFhMiDfIdVbcsBUIYt654MhOzJuwKMhZc04Q?e=gn06nJ 

Here is a basic picture of a pivot table I'm using: 

Thanks for your help!