In the given figure, you need to draw opposite ray to any of the rays −−→OP,−−→OQ,−−→OR or −−→OS
Draw ray −−→OT so that ←−−→TOQ is a line. Now, ray OP stands on line ←→TQ.
Therefore, ∠TOP+∠POQ=180o .... (1) (Linear pair axiom)
Similarly, ray −−→OS stands on line ←→TQ.
Therefore, ∠TOS+∠SOQ=180o .... (2) (Why?)
But ∠SOQ=∠SOR+∠QOR
So, (2) becomes
∠TOS+∠SOR+∠QOR=180o ..... (3)
Now, adding (1) and (3), you get
∠TOP+∠POQ+∠TOS+∠SOR+∠QOR=360o ... (4)
But ∠TOP+∠TOS=∠POS
Therefore, (4) becomes
∠POQ+∠QOR+∠SOR+∠POS=360o