Sure, here is the dialogue filled in with the correct forms of "will" and "going to":
5 Complete the dialogue with the correct form of will or going to.
Tara: Hi, Matt. Where are you going?
Matt: Into town. I 1 'm going to buy some new trainers.
Tara: I 2 will go with you. I can help you choose.
Matt: Thanks! Look, here's the bus now.
Tara: It's going very fast. I think it 3 isn't going to stop!
Matt: That's strange. Maybe it's full.
Tara: Hmm. I 4 'll phone my sister, Lucy. She usually drives into town on Saturdays. She 5 'll probably give us a lift. And her car is OK now, after the accident.
Matt: Accident? Actually, I think I 6 'm going to buy a bike.