The slope of that equation is (1/3)x. To find the perpendicular slope of a slope, you would have to find the reciprocal. To do this:
Flip the slope, and add a negative. It'll equal to -3x. Visual representation:
https://puu.sh/zPz5u/85fcdde6ab.png
now the perpendicular slope is -3, you will need to put this into point slope form, which is y - y1 = m(x - x1)
x1 = 5, y1 = -3
It'll equal to: y + 3 = -3(x - 5)
Now, you need to convert this to slope intercept form y = mx + b. All you need to do is just to distribute the -3 in that binomial, and move that 3 in the left side to the right side. It is easy!
Follow the representation, and there you go!
https://puu.sh/zPzak/d3ee776f3d.png
