As we go from (-6,6) to (9,1), x increases by 15 and y decreases by 5. Thus, the slope of this line is m = rise / run = -5/15, or m = -1/3.
Point-slope form: y-6 = (-1/3)(x+6), using data from (-6,6).
Slope-intercept form: starting with y = mx + b, substit. -6 for x, 6 for y and -1/3 for m:
6 = (-1/3)(-6) + b, or
6 = 2 + b. Then b = 4, and the equation in slope-intercept form is
y = (-1/3)x + 4.
