I have 3 questions concerning engagement level. I want to compute an engagement score by averaging the scores from these 3 questions and show it in a result chart. Is that possible? How?
There is no built-in functionality that you can use to perform this task – you would have to write a custom script.
The script would obtain the three responses (sgapiGetValue), perform the necessary math (https://help.surveygizmo.com/help/basic-math-using-scripting), and then place the calculated average (sgapiSetValue) as the response to a hidden question.
Concerning the result chart – assuming that you want you this to appear on a standard report you would just have to make sure that the hidden question is visible on the report. If you had something else in mind, some more custom scripting will be necessary.