一件商品按成本价提高80%后标价，然后再打9折销售，仍能获利6.2元，问这件商品的成本价是多少？若设这件商品的成本价为x元，则根据题意可列出方程为____ .

已知$\frac{a+b}{3}$=$\frac{b+c}{4}$=$\frac{c+a}{5}$，求$\frac{a-b-c}{c-a+b}$的值．

阅读理解

    Remember Tony and Peter．the twin brothers who started singing at the age of five?The little boys are now twenty—five years old and will come back home for the first time since they left ten years ago．They will sing to celebrate the 100th birthday of our beautiful town．

    Tony and Peter are famous for their wonderful voices．They are popular with both young and old people．Three years ago,the brothers organized the Garbage Can with their three cousins．The five of them started to write their own songs and have become successful．In the coming concert in Greentown,the Garbage Can is going to sing their bestloved songs and several new ones．

    The concert will be at Apple Park at 7 pm on 10th october．Fans who do not want to miss it should get to the park as early as possible．

当-$\frac{\mathrm{\pi }}{2}$$\le$x$\le$$\frac{\mathrm{\pi }}{2}$时，函数f（x）=sinx+$\sqrt{3}$cosx的（　　）