6
2 played ('a' is a vowel before 'y' so the 'y' doesn't change)
3 planned ('a' is a short vowel, so we write double 'n')
4 travelled ('l' at the end of verbs is always doubled)
5 opened (no need to double 'n' because the first syllable is stressed)
6 happened (the ending is -ed)
7 studied ('d' is a consonant before 'y', so the 'y' changes into 'i')
7
2 bought
3 chose
4 fell off
5 wore
6 wrote