Deeply conservative and simply has it in a bank account where he earns 3% interest. Andrew has?

... liabilities of 7000. He owes 5,000to the bank and pays 7% interest on this. When the bank would not lend him anymore, he used his credit card up to the limit and now owes 2,000 on that. The card’s rate of interest on unpaid amounts is 24%.

What could be a reasonable reference rate to use?
What is the value of FISIM paid by each of the twins in a year, assuming Andrew doesn’t borrow any more but cannot repay anything either.

Alex and Andrew are twins but quite unlike one another. Alex has assets of 10,000. He is deeply conservative and simply has it in a bank account where he earns 3% interest. Andrew has liabilities of 7000. He owes 5,000to the bank and pays 7% interest on this. When the bank would not lend him anymore, he used his credit card up to the limit and now owes 2,000 on that. The card’s rate of interest on unpaid amounts is 24%.

What could be a reasonable reference rate to use?
What is the value of FISIM paid by each of the twins in a year, assuming Andrew doesn’t borrow any more but cannot repay anything either