How would you answer this?

Question

Name all the sets to which negative 43 belongs to??

Answer 1

Let U be te set of all sets
The sets you are looking for are entirely charaterised by :
{ s element of U where the intersection of s with {-43} is not empty }

Answer 2

what's the context? there are uncountably many such sets, but i have a feeling you're only working with the most common sets

-43 belongs to the Integers, Rational Numbers, Real Numbers, Complex Numbers, Algebraic Numbers, etc.

but it belongs to any set that contains the number -43. for instance, {-43} is a perfectly valid set. as is {-43, 1.5} or {-43, -27, 5, 8, 100} or any such thing like that.