Explanation

The original statement is a direct quote, whereas the correct answer is a reported speech, which is a more polite and formal way of expressing the same sentence.

In reported speech, we change the sentence structure to:

"She asked him + question word + subject + verb"

So, the direct quote:

"Is it not your duty to help me in my old age?"

Becomes:

"She asked him if it was not his duty to help her in her old age."