Sure, here are the correct answers:

1. "Have you seen Helga?"
"She was here earlier but I haven't seen her **for** a while now."
2. Luke came across this old coin **by chance** while cleaning the attic.
3. I borrowed the money **from** the bank.
4. Would you like to help me **give out** these photocopies?
5. **Visitors** are allowed at the hospital between 5 and 8 pm.
6. Bright colours, **suit** people with dark complexions.
7. When buying something, never forget to ask for the **receipt**.
8. The Dragons, **beat** the Bulldogs in the football match yesterday.
9. My annual **income** is £30,000.
10. He is keen **on** buying a cat.
11. If you want to lose weight, you should **cut down** on fatty foods.
12. Can you **find out** what time the train leaves?
13. I really **get along** well with Sally. She is one of my best friends.
14. Don't forget to **give back** the book you borrowed from John.
15. I decided to contact him, **by phone** because it was the quickest way to reach him.