To get the slope of the line, you need to points. Two points you already have are (0,0) and (-5,6). So all you need to do is plug those points into slope equation (y1-y2 over x1-x2) 0-6 over 0+5 equals -6/5. The slope equals -6/5, and when you plug it into y=mx+b it equals y=-6/5x. Which is b.
