6.md

1. Modify the _buildRow function

Widget _buildRow(WordPair pair) {
  final alreadySaved = _saved.contains(pair);
  return ListTile(
    title: Text(
      pair.asPascalCase,
      style: _biggerFont,
    ),
    trailing: Icon(
      alreadySaved ? Icons.favorite : Icons.favorite_border,
      color: alreadySaved ? Colors.red : null,
    ),
    onTap: () {      // Add 9 lines from here...
      setState(() {
        if (alreadySaved) {
          _saved.remove(pair);
        } else { 
          _saved.add(pair); 
        } 
      });
    },               // ... to here.
  );
}