Newton has a total of 6 debts that need to be repaid.
1) 60 Coins to the Debt Bot to turn on the electricity in Newton's Lab at the start of the level
2) 60 Coins to the Debt Bot to turn on the broadband in Newton's Lab after clearing Carnivore Cove
3) 60 Coins to the Debt Bot to reopen the Shop in Lava Falls
4) 50 Coins for the Battery to the Venus Debt Trap in Venus's Lair
5) 40 Tax Tokens to the Giant Tax Bot in Newton's Lab after finding the Battery
6) 75 Coins for the Gyroscope from the Venus Debt Trap after clearing Bird Bay.