For 7-9, name the property that justifies each statement.
7. If AC = AB + BC and AC = BD, then BD = AB + BC.
8. If JL = JK + KL and JK + KL = MN + NP, then JL = MN + NP.
9. If m∠ABC + m∠ABC = m∠DEF + m∠ABC, then m∠ABC = m∠DEF