Match each number with its correct letter according to the picture
1. ray st is perpendicular to ray sr.
a) substitution
2. ∠rst is a right angle.
b) subtraction property of equality
3. m∠rst = 90°
c) definition of perpendicular lines
4. m∠1 + m∠2 = m∠rst
d) angle addition theorem
5. m∠1 + m∠2 = 90°
e) definition of right angle
6. m∠1 = 90° - m∠2
f) given