2D+E
---- = A
7C-B

2D+E=A(7C-B)

2D+E=7AC-AB

(2D+E)-7AC= -AB

  2D+E-7C   =B
- ---------
       A

PS:有個 -  係前面
____________

7C-B
---- = E
2D+E

7C-B=E(2D+E)

7C-B=2DE+2E

7C-B=2E(D+1)

7C-B
---- =D+1
2E

7C-B
(-----)-1=D
  2E

望可以幫到您...如我有錯..請他人更改我的錯處^^