A person has $20,000 in cash and has a debt of $20,000 with an annual interest of 6%, will you advise him/her to invest in the stock market for a 10% annual income or pay of their debt?

There’s no fixed rate in the stock market. Hence, there’s no guarantee that an individual will get 10% interest in such an investment. Although, stocks are usually profitable, but it’s based on experience.

I would only advice business loans, and not loans on speculations of some sort.