Which economic principle can be seen at work in the success of merchants such as Levi Strauss during the California Gold Rush?

The economic principle that is most observable in the success of merchants such as Levi Strauss was the supply and demand principle

The reason for this was that he was looking for gold at a time where it was limited and where a lot of people wanted to have gold but weren't willing to go and look for it in the wilderness for example.

it's not the readmission

the answer for 3 is b and the answer for 4 is d