Final answer:
In the expression 9x - 21 + x², the coefficient is 9x.
Step-by-step explanation:
In the expression 9x - 21 + x², the term 9x represents a coefficient. A coefficient is the numerical factor in front of a variable or the constant term. In this case, 9x is the coefficient of the x term. The coefficient indicates the number of x's being multiplied together.
Learn more about Coefficients in an algebraic expression