Suppose There Is a Linear Relationship Between the Number of Hours

Suppose there is a linear relationship between the number of hours per day that Michael spends on social media and his average grade.If Michael spends one hour per day on social media,his average grade is 90; if he spends 9 hours per day his average grade is 40.What is the slope of the function if hours on social media is plotted on the horizontal axis and grade is plotted on the vertical axis?

A) -2.25
B) 2.25
C) -6.25
D) 6.25
E) 0