Im having truble with this what is b+a+4

Anyone know? is appreciated! will mark brainliest if correct!

Can someone check if i did this correct. it’s number 4 if you’re wondering.

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.