First off: we need to find the slope. You can do that by taking a x over a negative y. In this case, that will be 1/3
Next: you put what you know into the appropriate form. As you have a point and a slope, you'll need the point-slope intercept form. This is: y-y1=m(x-x1). Everything plugged in looks like: y-5=1/3(x-3)
Finally: you solve. You first take 1/3 and distribute it across the parenthesis. That gives you y-5=1/3x-1. Then, you get y by itself.
Your answer is: y=1/3x+4