The words below can be anagrammed into new ones if you add the same extra letter to the end of the new word. Can you determine the added letter and the new words?

REAL + ?
TORAH + ?
COMPEL + ?
CLAIM + ?
NASTY + ?
HOBOES + ?

Answers:

The added letter is X, and the new words are:

RELAX
THORAX
COMPLEX
CLIMAX
SYNTAX
SHOEBOX