Angles 1 and 3 are corresponding angles, then they are congruent, that is,
m∠3 = m∠1
Substituting with data:
m∠3 = 120°
Angles 2 and 3 are same-side interior angles, then they are supplementary, that is,
m∠2 + m∠3 = 180°
Substituting with the previous value:
m∠2 + 120° = 180°
m∠2 = 180° - 120°
m∠2 = 60°