Calculating the average of two selected filters

[lucasx15]

Hello everybody !

I would like help in the following situation, I currently have two objects in my qvw (box and line graph) that calculate the customer satisfaction survey in our store.
It works as follows , the user selects two filters in a box and the chart plots the two selected items grouped by month/year. I used GetFieldSelections to develop this.

However, I would like to know how I can make it so that, when selecting two filters, the graphs also show the average of the selected items. For example:
When selecting Dinner 2 and Room Center, the average of the selected ones appears. Or when selecting Dinner 2 and Signals, display the average of the two items.