How do you catch legendary Pokemon in world 7.6?

It seems you're asking about catching legendary Pokémon in a specific version of the Pokémon games. However, "World 7.6" isn't a recognized version of any Pokémon game.

To answer your question properly, I need a little more information:

* Which Pokémon game are you referring to? (e.g., Pokémon Red, Blue, Yellow, Gold, Silver, Crystal, etc.)

* Which legendary Pokémon are you trying to catch? (e.g., Articuno, Zapdos, Moltres, Mewtwo, etc.)

Once I have this information, I can help you find out how to catch those legendary Pokémon in that specific game.