How many users answered the question No.20?
question No.20 refers to QuestionID = 20
SELECT MAX(UserID) - MIN(UserID) + 1 FROM Answer WHERE QuestionID = 20
database name:db_id mental_health_survey
Question table Question Cols: question text dtype text, question id dtype integer, 
Survey table Survey Cols: Survey ID dtype integer, Description dtype text, 
Answer table Answer Cols: Answer Text dtype text, Survey ID dtype integer, User ID dtype integer, Question ID dtype integer, 
