Final answer:
In the book 'Wonder', Via's father believed that she was old enough to take the subway by herself because she had shown maturity and responsibility. This decision allowed Via to gain independence and self-confidence.
Step-by-step explanation:
In the book 'Wonder', Via's father said she was old enough to take the subway by herself because he trusted that she had gained enough maturity and responsibility to handle it safely. By allowing Via to take the subway alone, he was giving her an opportunity to gain independence and self-confidence. This shows that Via's father believed in her ability to make responsible decisions and navigate the world on her own.