Averaging across different dimensions

[#1]

Hi,

This is probably very basic but I am really stuck with the below and would appreciate anything here:

I have 2 tables:

Table 1 has these 3 headers: Salesperson, Date, Quantity

Table 2 has these 2 headers: Salesperson, Sales Boss

Salesperson is the primary key across tables.

I want to create a bar chart with timeseries of average units sold per salesperson every month. This is a basic chart and is easy. Now I want to create a chart with timeseries of average units sold per sales boss every month. This is the part I am getting stuck as I cannot link across the different dimensions.

Ideally the chart should look like below: (Post this, I want to create another chart that has average units sold per sales boss per day). So need to create 2 charts here.