Chapter 13 - Periodic Functions and Trigonometry - 13-2 Angles and the Unit Circle - Practice and Problem-Solving Exercises - Page 840: 23

$150^\circ$

Angles coterminal to angle $\theta$ are given by $\theta \pm n\times360^\circ$ where n is an integer. Therefore, an angle coterminal with $-210^\circ$ that is between $0^\circ$ and $360^\circ$ is $$-210^\circ + (1)360^\circ = 150^\circ$$