goahead

以我所知~這是香港中學二年級的標準課程

英文的方程解如下:
Let x and y be the amount of rabbits and chickens respectively.

equation 1: x+y=30
                       y=30-x
equation 2: 4x+2y=100

let y=30-x substitute to the equation 2

4x+2(30-x)=100
   4x+60-2x=100
              2x=40
                x=20

let x=20 substitute to the equation 1
20+y=30
      y=10

Therefore, there are 20 rabbits and 10 chickens.