how many people or how many persons?
6 people or 6 persons
The words 'people' and 'persons' can both be used as the plural of person, but they are not used in exactly the same way.
'People' is used in most ordinary contexts: : a group of people : "There were only about ten people.": "Several thousand people attended the pop concert.".
'Persons' tends now to be restricted to official or formal contexts, as in : "This vehicle is authorized to carry twenty persons.": "No persons admitted without a pass."
"This information should not be disclosed to any unauthorized persons."