7x-8+9[(x+2)/3-2],其中x=4/5

---

7x-8+9[(x+2)/枯茄数悄3-2]=7x-8+9[(x+2)/没毕察3-2]=7x-8+3*(x+2)-18=7x-8+3x+6-18=10X-20=10X0.8-20=-12

---

7x+3x-20=8-20=-12

---