Statements1 22 and 24 are vert, angles2. lines m and n intersect at P3. 22 and 23 are a linear pair423 and /4 are a linear pair5. m/3+ m2 4= 180

Substitution property
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