In which of the following functions would it be appropriate to use only positive integers for the domain? Select all that apply.

David estimated he had about 20 fish in his pond. a year later, there were about 1.5 times as many fish. the year after that, the number of fish increased by a factor of 1.5 again. the number of fish is modeled by f(x)=20(1.5)^x. create a question you could ask that could be answered only by graphing or using a logarithm.

Solve for x and select the correct answer

Ineed with question three. i don't understand how i'm supposed to achieve 3 marks.