Questions about area and linear equations

Please see my answer at hk.knowledge.yahoo.com/question/question?qid=7008080400836

2008-08-12 18:21:33 補充：
Let weight of apple candy = A, so weight of orange candy = 40 -A
Total Cost = 40A + 60(40-A) = 40A + 2400 - 60A = 2400 - 20A.
Selling amount = 40 x 81 = 3240.
So % profit = [3240 - (2400 - 20A)]/(2400 - 20A) x 100% = 50% Solving the equation, A = 12Kg, Orange candy = 40-12 = 28Kg.