Fast filing Frank's job is to file files for Files Inc. The company recently ran a report and found the following data about Frank, where $t$ is in hours and $f$ is the number of files that Frank has filed during his work day. Also, $f$ is twice differentiable function.
Because Frank tires as he works, the rate that Frank files decreases as the day goes on. Which of the following is a reasonable number of files that Frank could have filed during his workday between $0\le t\le 8$?