The two-column proof below describes the statements and reasons for proving that corresponding angles are congruent:

Step Statements Reasons
1 segment UV is parallel to segment WZ Given
2 Points S, Q, R, and T all lie on the same line. Given
3 m∠SQT = 180° Definition of a Straight Angle
4 m∠SQV + m∠VQT = m∠SQT Angle Addition Postulate
5 m∠SQV + m∠VQT = 180° Substitution Property of Equality
6 m∠VQT + m∠ZRS = 180° Same-Side Interior Angles Theorem
7 Substitution Property of Equality
8 m∠SQV + m∠VQT − m∠VQT = m∠VQT + m∠ZRS − m∠VQT
m∠SQV = m∠ZRS Subtraction Property of Equality
∠SQV ≅ ∠ZRS Definition of Congruency

What is the missing statement for step 7?