“How much do I need to pay?”
I asked her how much…
This is reported speech and a quoted, or indirect, question. Two rules apply:
- Make the verb match the tense of the reporting verb, “asked” (change it into the past tense)
- Use sentence order, not question order in the quoted question part.
There is one correct answer. However, you may find the others used, too, and by people who speak perfect English. Why?
First of all, we sometimes quote direct questions and it’s not always easy to hear the quotation marks! Just think of this line from Paul Simon’s “50 Ways to Leave your Lover”: “She said why don’t we both just sleep on it tonight.”
And secondly, we adapt the tense in the reported speech to our frame of reference, which can be wider than just the situation at the time of speaking.
- I asked her what she was talking about. (The frame of reference is the situation at the time.)
- I asked her when she was/ is planning to move. (The frame of reference is is wider than just the situation at the time.)