Mr Potter had repaired his car yesterday. Our grandma had baked a carrot cake by 6 o’clock yesterday. He had written an

1. Mr Potter had repaired his car yesterday.
This sentence is in the past perfect tense. The past perfect tense is used to indicate that an action was completed before another past action or point in time. In this case, the action «repairing the car» was completed before the past point in time «yesterday». So, it means that before yesterday, Mr Potter had already finished repairing his car.

2. Our grandma had baked a carrot cake by 6 o’clock yesterday.
Again, this sentence is in the past perfect tense. It states that our grandma completed the action of baking a carrot cake before 6 o’clock yesterday. So, she finished baking the cake sometime before the specified time.

3. He had written an article by Monday morning.
This sentence also uses the past perfect tense to show that the action of writing the article was completed before Monday morning. So, by Monday morning, he had already finished writing the article.

4. Tim and Betsy were in Peru three years ago.
This sentence is in the simple past tense. It describes an action that happened at a specific point in the past, which is three years ago. The action is that Tim and Betsy were in Peru at that time.

5. Had you watered the flowers the day before yesterday?
This sentence is in the past perfect tense and uses the question form. It asks whether the action of watering the flowers was completed before the day before yesterday. So, it is asking if the person had already finished watering the flowers before the specified time.

In summary, the first three sentences talk about completed actions in the past using the past perfect tense. The fourth sentence describes an action in the simple past tense, and the fifth sentence is a question about a completed action in the past using the past perfect tense.