When looking at the graph we see that the temperature (y-axis) starts at 80 degrees. To find the slope, or how much it decreases and how often, we find the difference between 80 and the temperature it dropped to which is 77.5 . We also see it dropped this much after 1 hour which means each hour it drops -2.5 degrees so the correct answer is C.
For a parallel line the slope of the lines/equations will be the same but for perpendicular line the slope will be the negative reciprocal -(1/4)*x+b b=2-(-1/4)*8
