Need help with Data modelling and Running Total

Hi I need help with data modelling, based on my knowledge so far, i was able to create a star model between my dimesnions and fact table. I am trying to create a running total meausre but i noticed i dont have access to the columns from the other tables. kindly help. Here is the link to the PBIX file sample model.pbix

The running total is calculated as 'Inventory'[Sum of Inventory Value]+ Detailed Messages[Sum of Quantity Available] + 'Open Orders'[Sum of Units - Order/Transaction Quantity] - Demand Pegging [Sum of Quantity Ordered]

this will be the based total and the addition will start from there. Find the calculations in excel link calculations.xlsx