Substitution property
Step-by-step explanation:
m∠2 and m∠3 = 180
m∠2 + m∠3 = 180
m∠3 and m∠4 = 180
m∠3 + m∠4 = 180
for m∠2 + m∠3 = m∠3 + m∠4
Then m∠2 will be equal to m∠4
m∠2 = m∠4 (vertical anlges)
m∠3 = m∠3
since we can susbtitte m∠2 for m∠4 and vice versa,
the reason m∠2 + m∠3 = m∠3 + m∠4 is as a result of substitution property