Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$b$.
We know that $\lim\limits_{x \to a} k(x)=k(a)$, where $a$ as a constant. Thus, in the given statement, we have: $\lim\limits_{x \to c} b=b$ Thus, the answer is $b$.