how the hell should i know?

Ok. It is quite easy for me. If you have been collecting bananas properly in the first 3 levels, you should have 15 banana medals. Cranky will let you play his jet pack game.

Stradegy:

1.Build up the rocket. Try not to fuel it
2.When you built the whole rocket up, the fuel and bonus items appear. Collect the bonus item all the way as it will fall again everytime you take one until you have 5000 points or more. When you have a score of 5000 or more, a rareware coin drops. Take it and it is yours.

you need 15 banana medals and play cranky's Jet Pac game. When you get to 5000 pts cranky will get you the rareware coin in return.

You have to get 15 banana medals and go to Cranky Kong. He will let you play the Jet Pac game. You have to get, I think, 5000 pts to get the rareware coin.