Chapter 12.5, Problem 42E

To determine

To calculate: The rate at which average study timing decreasing where the production formula for s student’s performance on a difficult English examination is provided by $g=4hx-0.2h^2-10x^2$ where $g$ represents the expected grade of the student, $h$ represents time in hrs spent studying for the examination, and $x$ represent the student’ average grade point average and the teacher discerns that the student’ grade point averages stayed the same at $3.0$ of through the years and the student now spends an average of $15$ hours on daily study in a year for the examination, whereas the scores on the examination have dropped at a rate of $10$ points per year.