To solve this question, you’ll have to make a few assumptions.
You assume that you are constantly walking at 3 mph. Since your dog is twice as fast as you, its speed must be a constant 6 mph. Both you and the dog are out for an hour, so you must have walked 3 miles and your dog must have run 6 miles during this time. Your dog runs around you, so that’s why it covers more distance than you do.
You can break this problem down, line by line using Omerus as shown below:
Your walking speed (mph)
Length of time you and your dog are out for a walk (hour)
Your walking speed multiplied by 2 (your dog is twice as fast as you) = your dog's speed
Your dog's speed (mph) x time out for a walk (hour) = 6 miles distance covered by your dog