code: public double getTotalDistanceForTrips (Collection<Trip> trips) {
          TDoubleList distances = new TDoubleArrayList();
          for (Trip trip : trips) {
              distances.add(feed.getTripDistance(trip.trip_id, false));
          }
  
          return distances.sum();
      }
docs: Get total revenue distance (in meters) for set of trips.
  @param trips
  @return total trip distance (in meters)