Respostas

2014-05-24T16:05:47-03:00
=19-(3+12-6)+ 9 
=19-(15-6)+9
=19-9+9
=19
2014-05-24T16:09:53-03:00
19-(3+12-6)+9
19-(3+12=15-6=9)+9
19-9+9=19.