Here's why:
* Tribute Summoning Basics: Tribute Summoning generally involves sacrificing monsters on the field to summon a monster with a higher Level.
* Level Requirements: The number of monsters you tribute to summon a monster must match or exceed the monster's Level.
* Level 7 Monster: To Tribute Summon a Level 7 monster, you need to tribute at least 7 monsters.
Therefore, you need to tribute at least 7 monsters to summon a Level 7 monster.