Hi, jenchin66 welcome to the forum.
The answer they gave was 2519... Days later when the competition aired again, the answer was given as 3,406. It has been suggested that you also have to count ?'Roman Numerals' i.e. m=1000. As they NEVER give details about how they reach the answer. I would suggest it part of a ?'con' to get as many people as possible to part with their money.
Take another example:
Northampton 115 miles
Coventry 136 miles
Reading 71 miles
Margate 36 miles
Add all miles
The answer was 430 -