My teacher gave me an exercise which is adapted from the book "Macmillan Advanced Language Practice with key"
Complete the second sentence so that it has a similar meaning to the first sentence, using the word given. Do not change the word given.
(a-1) Tony knew what the answer was after reading the book. (read)
(a-2) By the time Tony ____________.
(Adapted) Source: https://studfiles.net/preview/1462020/page:19/
I understand the sentence a-1 as: First, Tony read the book. Then, he knew the answer.
So, my rewrite in sentence a-2 is:
By the time Tony knew what the answer was, he had read the book.
However, when I checked the book's answer key, it said:
By the time Tony had read the book, he knew what the answer was.
I seem not to agree with the book's solution, because I understand that "by the time" means "earlier than or equal to the time"; as a result, for me, the meaning of the book's solution is that first, Tony knew the answer, then he read the book. And it isn't similar in meaning to the original sentence.
Could you kindly tell me whether I correctly understand the meaning of the book's solution?