So if it goes through point (6, -1) and has a slope of -1/3, all of this is parts of the slope intercept equal, Y = mx - B. You have the slope, which is m in the equation, y = -1/3 x - b. you already have a y and x which are the points passed, -1 = -1/3 * 6 - b, but this can't equal y, so you must have did it wrong, the only way this could equal y is if the slope wasn't negative, and in that case it would be -1 = 1/3 * 6 - 3. Because 1/3 * 6 is 2 and then subract 3 and you get -1.
