In Chapter 53, Pip is attacked by Orlick at the marshes. Orlick throws a noose over Pip's head and ties him down. Afterwards, he proceeds to detail why it is that he hates Pip so deeply. Therefore, Pip is able to learn a great deal about Orlick in this scene.
Pip learns that Orlick blames him for getting between him and the woman he loved. He also believes Pip to be responsible for Mrs. Joe's death (as Orlick killed her to get back at him). Finally, Orlick reveals that he is connected to Compeyson and that he has solved the mystery of Magwitch.
To answer this, we try to list the possible ages of his children. Given above,
xyz=72
That first clue is not sufficient to produce a single solution, so Bob reveals the sum of their ages to Mark (sums sorted in ascending order):
Age1 Age2 Age3 Sum
3 4 6 13
2 6 6 14
3 3 8 14
2 4 9 15
2 3 12 17
1 8 9 18
1 6 12 19
2 2 18 22
1 4 18 23
1 3 24 28
1 2 36 39
1 1 72 74
Mark says that there is still insufficient information, there must be duplicate sets of ages that produce a single product. Here are the two:
Age1 Age2 Age3 Sum
2 6 6 14
3 3 8 14
I think the correct answer are 2, 6, 6.