Simple Linear Regression for sales prediction

[alenb]

There are 3 things I'd need to address.

1. Preparing the data to show the cumulative per-day sales

I'm trying these two approaches in the table, but it is not accumulating sales by the Date.

Aggr((Sum(Sales), Date), Date)

RangeSum(Above(Sum(Sales), 0, RowNo()))

2. Actually using the data for linear regression. This actually seems the easier part.

Planning to use LinEst_M for slope and LinEst_b for intersect, LinEst_R2 for analysis. 

3. Visualizing the line as in excel below.

Sample data:

Excel line rendering: