a. The coordinates of the first train are (-12,6), and those of the second train are (20, 35)
b. The slope is the x-axis distance divided by the y-axis distance, or [tex] \frac{rise}{run} [/tex].  Therefore, the slope is [tex] \frac{6}{-12} [/tex], or -0.5.  It is neither horizontal or vertical.  The line equation could be presented as the following:
Slope intercept:Â [tex]y=-0.5x[/tex]
Standard:Â [tex]y+0.5x=0[/tex]
c. Line equation: [tex]y= -\frac{1}{3} x[/tex]