no, its neither 21 or 19 because 9 and 10 together make 109, if you subtract 5 from 109 you get 104, there are a 104 days of summer vacation, thats also in phineas and ferb, phineas and ferb create things that go against the rules of physics, if the rules of physics were ever broken then society would collapse, but phineas and ferb have already done that so that means that society has already crashed so that must mean that nobody is around to care anymore so that question is irrelivent.
