A binomial is an algebraic expression that consists of exactly two terms. Let's analyze each given expression:
1. [tex]\(-8\)[/tex]: This is just a single constant term, so it is not a binomial.
2. [tex]\(7a\)[/tex]: This is a single term with a coefficient and a variable, making it a monomial, not a binomial.
3. [tex]\(3 + 4x\)[/tex]: This expression consists of two terms: a constant term [tex]\(3\)[/tex] and a term involving a variable [tex]\(4x\)[/tex]. Therefore, it is a binomial.
Based on this analysis, the correct answer is:
3
