Translation:I buy bread at a quarter to seven.
I wrote, "I buy bread at 15 minutes before 7" which is also equivalent, but was marked wrong.
When you want to talk about time, you can use vào lúc or lúc equivalently to "at" (in another way, the word vào in vào lúc is optional). They are the same.
- Tôi sẽ ăn trưa (vào) lúc mười một giờ. - I will eat lunch at eleven (o'clock).
- Họ đến nhà ga (vào) lúc sáu giờ kém hai mươi. - They arrive at the train station at twenty to six.