Ken's house is twice as far from Dawn's house as Mary's, so the distance between Ken's and Mary's is half that between Ken's and Dawn's (4 miles) which means the former is (1/2)*4 miles = <<4*1/2=2>>2 miles
If Ken goes from his house to Dawn's, he has covered 4 miles
He goes from there to Mary's (2 miles, same as Ken's to Mary's) for a total of 4+2 = <<4+2=6>>6 miles.
He goes back to Dawn's (another 2 miles) for a total of 6+2 = <<6+2=8>>8 miles
Then he goes to his own house (4 miles) for a final total of 8+4 = <<8+4=12>>12 miles
#### 12