y=mx + b is equation of a line. The slope of the line is "m" and the y-intercept is "b". We can get the equation of the line given the slope and y-intercept or given two points (x1, y1) and (x2, y2). If given two points, use the formula (y2 - y1)/(x2 -x1) to find the slope. Then use the slope and one of the coordinates give to find "b". Then you have the slope and y-intercept needed to write the equation.