Problem 9.2. In four classes of a school, there are more than 70 children, all of whom came to the grade meeting (no other children were present at the meeting).

Each girl who came was asked: "How many people from your class, including you, came to the meeting?"

Each boy who came was asked: "How many boys from your class, including you, came to the meeting?"

Among the answers, the numbers $7,9,10,12,15,16,19$ and 21 were encountered (all children answered correctly).

(a) (1 point) How many children are there in the largest class of the grade?

(b) (3 points) How many girls came to the grade meeting?