Sonia has a sports collection. She has ten tennis rackets, seven basketballs, four volleyballs and five soccer balls. She plays tennis every day she is in the school tennis club. Susan also has a sports collection. She has five baseballs, six volleyballs, three ping-pong bats and many ping-pong balls. Oh, she also has two soccer balls. But she doesn't play sports. She only watches them. Sandy doesn't play sports, and she doesn't have balls. Sonia and Susan have  _  volleyballs.
4 6 10 12