How can a father be advised to get rid of usurious money he acquired decades ago, and what should he do with the unlawful money if he does not know its amount?

We previously discussed the ruling on depositing money in usurious banks, the ruling on the returns, and how to dispose of them. If the exact amount of money taken from prohibited interest is unknown, then one must strive and disburse what is most likely to clear one's conscience.