What is the meaning of “My cat was back and so was I”? Had the author gone anywhere? Why does he say that he is also back?

What does he say about Lutkins?

A man borrowed Rs 40,000 at 8% simple interest per year. At the end of second year he paid back certain amount and at the end of fifth year he paid back Rs 35960 and cleared the debt. What is the amount that he paid back after the second year?