None of the reasoning provided justifies why m∠ABC is either 55° or 25°.
To find the measure of angle ABC, we can use the fact that the sum of the measures of adjacent angles is equal to the measure of the larger angle formed by the two adjacent angles. In this case, angle ABC is the larger angle formed by angles ABD and DBC.
So, we have:
m∠ABD + m∠DBC = m∠ABC
Substituting in the given measurements, we have:
15° + 40° = m∠ABC
Simplifying, we find:
55° = m∠ABC
Therefore, the measure of angle ABC is 55°.