You can find the slope by using the formula m=y2-y1/x2-x1.
So in this situation, the y2 will be -9 and the y1 will be 6. x2 will be -6 and x1 will be -9. After you find that out and plug the numbers into the formula, you will get -15/3 and you can simplify it. In the end, you will get the slope of -5.