How can the y-intercept of the line be interpreted?

If f(x)= sqrt4x+9+2, which inequality can be used to find the domain of f(x)?

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.

Which expression gives the exact value of x?