Ответ:

  1. Did Lena and Adam use to ask Gran questions about the world?
    Yes, they did.
  2. Did Lena and Adam use to have phones?
    No, they didn’t.
  3. How did Gran use to communicate?
    She used to communicate by talking to people and writing letters.
  4. Did the postman use to bring a lot of letters?
    Yes, he did.

Questions use Did + subject + use to + base form. Short answers use did or didn’t.