code: void subtractFlakes(int quantity) {
          for (int i = 0; i < quantity; ++i) {
              int index = numFlakes - i - 1;
              flakes.remove(index);
          }
          setNumFlakes(numFlakes - quantity);
      }
docs: Subtract the specified number of droidflakes. We just take them off the end of the
  list, leaving the others unchanged.