If this is the question, there is an answer at the back of the book. If you don't understand, you can change your mind. The answer is as follows:
The return journey of Line A is 18km, so it is more than that of Line B 18 * 2 = 36 (km) and more than that of Line B 1 hour. If it takes the same time as that of Line B, it is 36- 12 = 24 (km) more than that of Line B, and A is 65444.