I have the answer in this picture. But im not sure if this might be really what your asking for.
Your slope would be -1/4x. If you look at the y-intercept on your graph, which is -2, you would start to count up one box and over 4 boxes to the left. We call this rise/run. So knowing what the slope is now, your entire equation would be y= -1/4x - 2. (Also, if the line is going up towards the left it is a negative slope, if it's to the right it is positive.) I hope this helps love! :)
The pair of numbers that would have 20 as their lcm is 4 and 5