The normal use of ∈ ("belongs to") in the representation of a set is to define the category of the variable x. For example x∈ℤ would mean that x is an integer, that is, x belongs to the set of all integers; x∈ℝ would mean that x is a real number (that is, not complex), that is, x belongs to the set of all real numbers. So the symbol ∈ is used to say "x belongs to the set of ...". x∈1 does not make any sense to me as used in this context, because "1" is not a set. If it were intended to be a set it should appear in braces: "{1}", in which case the tabular form would be {1}, because 1 lies in the interval (-3,3). This defines the set B, and below are more examples of how this set could be defined.
If B={ x : x ∈ ℤ, -3 < x < 3 } then the tabular form would be:
B={ -2, -1, 0, 1, 2 } which is integers between -3 and 3 (exclusive).
If B={ x : x ∈ ℕ, -3 < x < 3 } then the tabular form would be:
B={ 1, 2 } which is all natural numbers between -3 and 3 (exclusive).