Forecasting in Tableau where data is on MAS server (cubes)

I have a tableau question (about modeling). I have built a workbook that shows Daily Sales for the current month (two columns – current year and last year’s daily sales). I have added three lines – current and last year’s daily sales budget, and last year’s daily sales average. I would like to add a fourth line that shows the budget realization forecast for the remaining days in the month. This line would show the sales number for each of the next x-amount of days to achieve the monthly sales budget. Is it possible to create this type of line? Maybe through a custom reference line? Data connection is through MAS server, I am new to this and data server connection. I have attached an example titled Realization Forecast Example (someone explained this to me via simple excel concept). I am attaching the screenshots (with the titles: Real workbook snapshot) from the original Tableau workbook I am working on, as I can' share it due to privacy reasons. Let me know if any additional info needed.