Question 28410
12b-[9-7(5b-6)]
=12b-[9-35b+42]
=12b-[(9+42)-35b] using additive commutativity and then associativity
=12b-[51-35b]
=12b-51+35b
=(12b+35b)-51   using additive commutativity and then associativity
=47b-51