Answer:
The green box is -3
Explanation:
You are reading from a graph, so it is more important perhaps, to pick clear points rather than easy to handle points.
The easiest two points you could use would be
(0,4)
(1, 1)
Slope
m = (y2 - y1)/(x2 - x1)
y2 = 4
y1 = 1
x2 = 0
x1 = 1
m = (4-1)/(0 -1)
m = 3/-1 = - 3
Y intercept
b = 4 from the point 0,4
Line
y = - 3x + 4