Which of the following is an example of a mathematical expression?

A mathematical expression is a combination of numbers, variables, and operators (such as addition, subtraction, multiplication, and division) that represents a value. It's important to differentiate between expressions and equations or inequalities, which make claims about the equality or inequality between two expressions.

In the given options, the correct choice includes a variety of individual terms that do not assert any equality or inequality. For example, the option mentions "8," "15x," and "4n - 2," which are considered individual expressions that can represent values on their own rather than forming an equation or inequality. This collection of terms makes option C an example of a mathematical expression rather than a statement of equality or inequality.

The first two options represent equations and inequalities respectively, while the fourth option is a specific type of equation (the equation of a line). These forms are not just expressions since they assert a relationship between two mathematical components.