Put the equation in slope-intercept form: y = mx + b. Remember that m is the slope, b is the y-intercept and (x,y) is a point that the line passes through. When I substitute everything, it'll give me y = -3x + b. It passes through point (6,-1) so let x = 6 and y = -1. That gives me -1 = -3(6) + b. From there, I get -1 = -18 + b, so b = 17. Put everything together and you get y = -3x + 17.