As shown in the given figure
line a // line b ⇒ given
MR and NP are transversals
So, for ΔMOP and ΔRON, we can conclude the following
(1) ∠1 = ∠2 ⇒⇒⇒ alternative angles are congruent
(2) ∠ MOP = ∠ RON ⇒⇒⇒ vertical angles are congruent
(3) ∠ 4 = ∠ 3 ⇒⇒⇒ alternative angles are congruent
So, from 1,2 and 3
∴ ΔMOP ~ ΔRON by AAA-Rule