Explanation
Right Click on the Customer Name -> Create -> Set
Graphical user interface, text, application Description automatically generated

Create a calculated field:
Graphical user interface Description automatically generated

Drop the Top 20 by Sales set, Customer Name to Rows.
Drop Sales and Profit Ratio to the view. Format the profit ratio so it will show the percentage.
Graphical user interface, text, application, chat or text message Description automatically generated

Sort the Profit.
Table Description automatically generated

Cube data sources can only be used as the primary data source for blending data in Tableau.
All others are true.
Refer: https://help.tableau.com/current/pro/desktop/en-us/cubes.htm

While creating the parameter action, it is not mandatory to specify the aggregation.
All others are true.
Refer: https://help.tableau.com/current/pro/desktop/en-us/actions_parameters.htm

Create a Calculation to get the first alphabet of the customer name.
Graphical user interface, text, application Description automatically generated

Now drop the First Alphabet field to Rows and Quantity field to the Text on the Marks card. Change the aggregation from SUM to AVG. Your view will look like this:

Explanation
Go to the menu Dashboard -> Action -> Add Action

Select Filter, here you will find the Target Sheets

For all other options, you will not find the Target Sheets. Try it yourself.