usedn't

English as a Second Language English Vocabulary, Grammar and Idioms
1

1a. There used to be some trees in this field, usedn’t there?
1b. There used to be some trees in this field, usen’t there?
2a. Didn’t you used to live near me?
2b. Didn’t you use to live near me?
Please correct and comment.
Thanks.

2

1a. There used to be some trees in this field, didn’t there?
1b. There used to be some trees in this field, didn’t there?
2a. Didn’t you use to live near me?
2b. Didn’t you use to live near me?