how do you prove a parallelogram with given and proof statements

Question

given and proof statements-

given: <1 and <2 are supplementary; <2 and <3 are supplementary

prove: PQRS is a parallelogram

therom: same-side interior angles

Answer 1

angle 1 + angle 2 = angle 2 + angle 3

angle 1 = angle 3 <--- subtracts angle 2 from both sides

so the opposite sides are parallel by same-side interior angles

This forces the other pair of interior angles to be equal which

in turn causes the other pair of opposite sides to be parallel