EDIT: I forgot to mention the second condition: $a \leq c \leq b$.
I'm taking a first-year undergraduate calculus course and I'm faced with this problem. I'm not sure about how to proceed without using examples. I realize that $|c|$ might be greater than $b$ or $-a$ depending on the sign of each term.
If $c \geq 0$:
$$|c| \leq b \leq \max(b, -a)$$
If $c < 0$:
$$|c| \leq -a \leq \max(b, -a)$$