Answer:
20 Years.
Step-by-step explanation:
As you could see my friend owned a dog for 9 years, and it reads that it is one year less which is 10 years since 10-1 (aka one year) equals 9 so anyways we know it's 10, and it's twice as long 10 x 2 (aka twice). which is how I got my answer... 20!
