Here are the rewritten sentences:

7. Mac Kenzie will have finished his presentation **by** 11 a.m. tomorrow.
→ Mac Kenzie will have finished his presentation **by** 11 a.m. tomorrow.

8. We haven't been to a party for over a year.
→ We haven't been to a party for **a long time**.

9. I haven't been to an Indian restaurant before.
→ **This** is the first time I have been to an Indian restaurant.

10. In the middle of our dinner, there was a knock at the door.
→ **When** we were having dinner, there was a knock at the door.

And now for Exercise 6:

1. This is the first time he has gone skateboarding.
→ He hasn't **skateboarded before**.

2. She started learning to drive 1 month ago.
→ She has **been learning to drive for 1 month**.

3. We began walking when it started to rain.
→ We have **been walking since it started to rain**.

4. I last had my hair cut when I left high school.
→ I haven't **had my hair cut since I left high school**.

5. It is a long time since we last talked.
→ We haven't **talked for a long time**.

6. This is the first time I had such a delicious meal.
→ I haven't **had such a delicious meal before**.

7. I haven't received her letters for 8 days.
→ The last **time I received her letters was 8 days ago**.

8. We started learning English five years ago.
→ We have **been learning English for five years**.