How do you get into world 7 on new Super Mario Brothers on ds?

Answer 1

You need to get this blue mushroom and it will turn u very tiny like you're miniature then go to the boss at the end and beat him miniature size then instead of jumping over the gap go down in the gap and you run straight and the sign will flip and it will say w7 on it and you're there

or you can go to the cannon on world four