David decided to ride his moped across the country during his 12 week summer vacation. The route he took from Baltimore, MD to Tucson, AZ covered a...

David decided to ride his moped across the country during his 12 week summer vacation.  The route he took from Baltimore, MD to Tucson, AZ covered a total of 2315 miles.  To keep his mind occupied during some of the long flat stretches of countryside, he often did algebra problems in his head.  One day, for example, he determined that his distance from his starting point was exactly 85 miles less than twice the distance remaining until the finishing point.  How far was David from the finishing point of his journey when he made that calculation?  Start your work by defining the unknown quantities in terms of a variable.  Show all work and write a complete answer, including units