use both points to find the slope
[tex]\frac{y2-y1}{x2-x1}[/tex]
[tex]\frac{-13-3}{9-(-3)}[/tex]
[tex]\frac{-16}{12} =\frac{-4}{3} =slope[/tex]
Now, to find b, plug in one of the points in y=mx+b
3=[tex]\frac{-4}{3}[/tex](-3)+b
3=4+b
b= -1
therefore, your final equation should be,
y=[tex]\frac{-4}{3}[/tex]x-1
