(-5)×(-87/9)-(-7)×(＋79/9)+12÷(-9/79)
=5×87/9+7×79/9-12×79/9
=5×87/9+79/9*（7-12）
=5×87/9-5×79/9
=5/9×（87-79）
=5/9×8
=40/9不好意思，问题弄错了应该是(-5)×(-79/9)-(-7)×(＋79/9)+12÷(-9/79)(-5)×(-79/9)-(-7)×(＋79/9)+12÷(-9/79)=5×79/9+7×79/9-12×79/9=79/9*(5+7-12)=79/9*0=0