Sure, I'll help you complete the sentences using "will" or "be going to" and underline the clues that indicate which one to use.

6. You predict the landing of aliens on the earth in the next ten years.
Your friend: All this talk about aliens is complete nonsense, isn't it?
You: Is it? I think aliens **will** _(land)_ on the earth in the next ten years.
- **Clue:** "I think" indicates a prediction.

7. At first you were interested in a fitness class, but then you decided not to register.
Your friend: Have you decided what to do about the fitness class that was advertised?
You: Yes, I **am not going to** _(not/apply)_ for it.
- **Clue:** "Have you decided" indicates a prior decision.

8. The house was very quiet when I got home. Everybody had gone to bed. Your friend is noisy.
You: Shhh! Don't make so much noise. You **will** _(wake)_ everybody up.
- **Clue:** "Don't make so much noise" indicates an immediate consequence.

9. You know that Nancy has decided to get married.
Your friend: Have you heard about Nancy?
You: Well, I heard that she **is going to** _(get)_ married.
- **Clue:** "I heard that" indicates a prior plan or decision.

10. Sue and I have decided to have a party.
You: We **are going to** _(invite)_ lots of people.
- **Clue:** "have decided" indicates a prior decision.

11. A: Look! The boss is coming.
B: The meeting **will** _(take)_ place at 6 p.m.
- **Clue:** "Look! The boss is coming" indicates a spontaneous decision.

12. A: We don't have any butter.
B: Really? **I will** _(get)_ some from the shop then.
- **Clue:** "We don't have any butter" indicates a spontaneous decision.

13. A: Why do you need to borrow my bag?
B: I **am going to** _(visit)_ my best friend in Sai Gon next Monday.
- **Clue:** "next Monday" indicates a planned future event.

14. A: I'm really cold.
B: I **will** _(turn)_ the heating on.
- **Clue:** "I'm really cold" indicates a spontaneous decision.

15. A: Are you going to Jayce's party tonight?
B: Yes. Are you going too? I **will** _(give)_ you a lift.
- **Clue:** "Are you going too?" indicates a spontaneous offer.

16. A: Do you have any plans after you leave university?
B: I **am going to** _(work)_ in a company at Da Nang.
- **Clue:** "Do you have any plans" indicates a prior decision.

17. The phone rings.
A: I **will** _(get)_ it!
- **Clue:** "The phone rings" indicates a spontaneous decision.

18. A: **Are you going to** _(you/take)_ the children to the cinema this weekend?
B: I have seen some tickets on the table.
- **Clue:** "this weekend" indicates a planned future event.