Best Friends

• add a different letter to the start and the end (1)
• add a letter to the start (1)
• add a letter to the start and three to the end (6)
• add a letter to the start of someone from here (1)
• add a useful math abbreviation to the end (2)
• anagram (5)
• change the second letter (6)
• double (3)
• move the second letter first and multiply it by 10 (3)
• replace the middle two letters with one different letter (2)
• surround the last letter with two consecutive letters (4)
• transpose the last two letters (2)
• transpose the last two letters, and add an appropriate article to the end (6)

Remove a bigram and add a word to get the final answer.