Need help with one geometry question?!?

By the definition of supplementary angle, m1 + m2 = _____ (a) and m2 + m3 = _____ (b). Then, m1 + m2 = m2 + m3 by the ______ (c). Subtract m2 from each side. You get 1 = _____ (d) or 1 is equal to ____ (e). Plead help asap!!