Ratio of cat : to dog = 40 : 20 = 2:1
M= -8 - -5/ 3 - 15= -8+5/3-15= -3/-12 = 3/12 = 1/4
The slope is 1/4.
The slope formula is m=y2-y1/x2-x1. I plugged in -8=y2, -5=y1, 3=x2, and 15=x1. Then I solved it.
Do you have a specific equation I can help you with. I can explain them better with a problem to look at?