A book is 3.5cm thick and each cover is 1.8mm thick. how thick is the book without it's cover ​

Can someone answer it, and plot it, for 20 points and brainliest answer? p. s. they're the same ! : )

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.

Ithink i know it but i want to be sure so can you me out ?