Hint
Consonants and vowels (AEIOU) are each worth something.
Answer
12 miles away.
Consonants are worth 2 and vowels (AEIOU) are worth 3.
Double-Checking
York
3C + 1V = 3 x 2 + 3 = 9
London
4C + 2V = 4 x 2 + 2 x 3 = 14
Manchester
7C + 3V = 7 x 2 + 3 x 3 = 23
Leeds
3C + 2V = 3 x 2 + 2 x 3 = 12
??
Puzzle 3
The map below shows the street locations of a city. Position three police officers such that the entire length of every street can be seen by at least one officer.