(-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