I am preparing for the NY State Geometry Regent, and I answered a multiple-choice point/slope question. The question reads: What is an equation of the line that passes through (-9,12) and is
perpendicular to the line whose equation is y = 1/3x + 6?

The correct answer was: y = -3x - 15.

I went over the math once again after seeing the correct answer. I still got y = 1/3x + 15. I don't see how the answer is y = -3x - 15. Can someone please explain the problem to me?