If mZQOS = 57, mZPOR = 67, and mZPOQ = 28, what is mZROS?

Answer:
ROS = 18 ⁰
Step-by-step explanation:
QOR = POR - POQ
QOR = 67 - 28 = 39
QOS = QOR + ROS
ROS = QOS - QOR
ROS = 57 - 39 = 18