Hello Lang Sui,
I think a Level of Detail calculation will assist with the first Scenerio. The detail in the view is lower than the detail of the calculation so you will either need to utilize a Table Calculation or a LOD calculation.
Is it possible to share the workbook or portion of the workbook to assist with this?
In addition, you may wish to review the Data Revelations site for in-depth explanations of working with Survey Data in Tableau - www.datarevelations.com/category/visualizing-survey-data-and-likert-scales is a good place to start there.
I hope that helps.