Use either the distance formula or the Pythagorean Theorem. i suggest you plot the 2 given points and draw the line segment CD connecting these points.
What is the horiz. distance between the 2 points? The vertical distance?
If you'd square the horiz. distance and also square the vertical distance, and then add these two squares together, and finally take the positive square root of this sum, you'll have the distance cd. Round it off to the nearest tenth.
You would do 20-8= to 12 so the difference between the cat and dog is 12 ft
So from the blue triangle to the green triangle, we can see that the green triangle is smaller, therefore eliminating options A and B.
Now to find the scale factor, use one of the sides of both triangles. In this case, I'll be using the bases of both. The blue triangle's base is 10, while the green is 5.
Using this info, we can make the fraction , which can be further simplified to . This is the scale factor.
In short, the answer is the last option.