Sure, here are the correct forms of the words in the blanks:

1) How long is the **flight** from Rome to Paris? (fly)
2) Pulling my front tooth didn't hurt. - It was completely **painless**. (pain)
3) Actors have to **memorize** a lot of words when they are in a play. (memory)
4) The **quality** I like most about her is her kindness. (person)
5) **Luckily**, they invite me to watch their new film. It was fantastic. (lucky)
6) The new flat is not **affordable**. It is too expensive. (afford)