Ответ: When did you buy this tabled?

 How much did cost your new computer?

 What did you do after school yesterday?

 Why didn't you call me last night?

 Where did dad save the photos on the computer?

Which files did you delete?

How many copies did Gary print yesterday?

Which company did Steve Jobs help to start?

Объяснение: в вопросе мы используем DID и поэтому форма глагола у нас остаётся прежней!