The graph below shows the hours studied and the test grades on a biology test for 7 students. The red line on the graph can be used to approximate the test grade the average student receives for the number of hours he or she studies.

The grades on Biology Exam

(a)  Determine the slope of the red line using the two points indicated with ordered pairs.

(b) Using the slope determined in part (a) and the y-intercept, 10, 532, determine the equation of the red line. 

(c)  Using the equation you determined in part (b), determine the approximate test grade for a student who studied for 3 hours.

(d)  Using the equation you determined in part (b), determine the amount of time a student would need to study to receive a grade of 80 on the biology test.

100 (4, 96) 95 90 85 80 75 70 65 60 55 (0, 53) 50 1 2 3 4 5 Hours Studied Test Grade