When starting the level, you can adjust how many Coins the level costs. Increasing the level cost will also increase how many Stars you get when answering questions.

The increase in Stars happens immediately when answering questions, and doesn't have its own line in the end-of-total screens.

The chosen level cost will remain when you complete the level and go to start the next one. If you wish to change to a different level cost, you can do so by returning to the home screen.