pls. explain with a figure.

PQ is a line,

By linear pair axiom,

POS + ROS + QOR = 180^o

Now, QOR = 90^o

POS + ROS =  90^o ....... (1)

QOS - POS =  ROS + QOR - POS

Now, Using (1)

QOS - POS = ROS + QOR - POS

QOS - POS = ROS + QOR -  90^o +   ROS

Since, QOR =  90^o

QOS - POS = 2ROS