았어 if have batchim and last vowel is ㅏ or ㅗ, add 았어. If no Batchim and last vowel is ㅏ or ㅗ, combine with ㅆ and add 어. If no batchim and last vowel is ㅗ, combine with ㅏㅆ and add 어. If ends with vowel ㅡ, drop it and count the next last vowel. If have specific batchim ㅂ and last vowel is ㅗ, delete ㅂ and add 왔어