107.3e
If a spell or ability refers to the {X} or X in the mana cost, alternative cost, additional cost, or activation cost of another object, any X in that spell or ability’s text uses the value of X chosen or defined for the other object.
If a spell or ability refers to the {X} or X in the mana cost, alternative cost, additional cost, or activation cost of another object, any X in that spell or ability’s text uses the value of X chosen or defined for the other object.