angles that are across from each other at a junction are vertical angles, and thus equal.
∡4x is across the junction from ∡2x + 6, meaning those two sisters are twins.
angles that lie on the same flat-line are linear angles, and since a flat-line has 180°, then those linear angles are supplementary angles, namely they both add up to 180°.
we know x = 3, we also know that ∡4x + ∡y = 180°