Which set does 6 belongs to isn't rational numbers or what?

Answer 1

6 is a rational number and it belongs to any set that contains it!

It belongs to {6},

or {45, sqrt(2), 6, pi, -3/7},

or all whole numbers between -43 and 53,

or multiples of 2,

or composite numbers,

or counting numbers,

or integers,

or rational numbers,

or real numbers,

or complex numbers,

etc.