This is how the "Do" button looks after using the preceding technique:

  FlatButton(
    child: Text("Do"),
    onPressed: () {
      FavorsPageState.of(context).acceptToDo(favor);
    },
  )

And the corresponding acceptToDo(favor) method is done as follows:

void acceptToDo(Favor favor) {
  setState(() {
    pendingAnswerFavors.remove(favor);

    acceptedFavors.add(favor.copyWith(accepted: true));
  });
}

As you can see, it is almost the same as the refuseToDo() method; the only differences are in the target list and accepted status.