Help on finding groups with a similar count as one groupmember on a certain column

I have two tables:

1: A table Person (P) which contains (among others) the column
number

2: A table Ticket (T) which contains (among others) the columns number and penalty.

I need to make a query to find all persons with the same amount of tickets as a certain person. In other words, if the person with number x has y penalties, I need to find all other persons with y penalties.

I already formulated the query beneath:

SELECT P.number, COUNT(T.penalty) number_of_tickets
FROM Person D, Ticket T
WHERE T.number = P.number
GROUP BY P.number

I guess I need to use 'HAVING' but am not sure how to solve my query.

Anyone can help a newbie?

Maybe a screenshot will make the question more clear (screenshot did not happen, do not know/ am not able to post it here. transcripted it in text...):

------------------------------------------------------------------------
SELECT B.lidnummer, COUNT(B.betalingnummer) aantal_boetes
FROM Boete B
GROUP BY B.lidnummer

DATA OUTPUT:

lidnummer aantal_boetes
130 1
112 1
109 2
201 7
208 9
------------------------------------------------------------------------
My question is how I can extract the data with the same 'aantal_boetes' as 'lidnummer' 112.

So 'lidnummer 112' has 'aantal_boetes 1'
'lidnummer 130' also has 'aantal_boetes 1'

So how can I extract those (and in such a way that if 'lidnumer 112' had a different count of 'aantal_boetes' it would automatically adjust).

How would I change my query to get that info?

Thank you very much.

Just starting to learn making queries and did not yet get to the concept of using a query into a query (as in a second SELECT, FROM, WHERE part).

Thanks again!