The task is:
Read these two sentences. Chose the one where Mike has already planned
to invite Daisy to St.-Petersburg.
- I'm going to invite Daisy to St.-Petersburg.
- I'll invite Daisy to St.-Petersburg.
I think the second one is correct as we are talking about immediate decision. "To be going to"
is used for intention whereas he's just made up his mind. The key says about the first variant.
Best Answer
Actually there is not really enough context to say whether Mike has already decided to invite Daisy in one or the other of your sentences.
He might be saying to his friend
To choose the second over the first, you may be making some cultural assumptions, or assumptions about Mike. The only unambiguous phrasing might be
The only thing certain in all three scenarios is that Daisy may not know yet.