(a) In given example,
(b) When slope is positive then line slope will show upward in a graph. When slope is negative then line slope will show downward in a graph.
Here, slope is -3 which is negative. Hence, line slopes will be downwards in a graph.
(c) Linear regression equation is, y = -3x
Suppose x = 0 then y =0
If x = 1 then y = -3
Therefore, two points are (0,0) and (1,-3)
Following is the graph for above two points: