If in six years Tom's brother will be 30 years old, he is currently 30-6 = <<30-6=24>>24 years old.
Since Tom's brother is 4 times as old as Tom's dog, Tom's dog is 24/4 = <<24/4=6>>6 years old currently.
Tom's dog will be 6+6 = <<6+6=12>>12 years old in six years.
#### 12