The explicit formula for a straight line is written as y = Mx + b, where m is the slope and b is the y intercept.
The y intercept is the y value of where the line crosses the x axis. On the above picture the line crosses the x axis at -2, so the y intercept is -2
Use 2 points in the line for the slope:
Slope = change in y over the change in x:
(0,-2) (6,0)
Slope = (0- -2) / (6-0) = 2/6 = 1/3
Answer: y = 1/3x-2