What part of A Wrinkle in Time talks about solving problems?

Much of A Wrinkle in Time is about solving problems. For example, as the book opens, Meg is faced with many problems, such as the mystery of her missing father and how to deal with the complexities of her school life—for example, by learning not to get into fights when other students insult Charles Wallace.
However, an important place where a problem must be solved is near the end of the book, when Meg must go back to Camazotz alone to rescue Charles Wallace. At this point, it is up to her to figure out how to get her brother back from IT.
As she walks toward Central Central, she wonders how she can do this. Then it occurs to her to ask,

What have I got that IT hasn’t got? she thought suddenly. What have I possibly got?

At last, it strikes her that she has one thing the cold machine entity doesn't, which is love. When she realizes she can offer Charles Wallace her love, she is able to rescue her beloved brother.