I have another question! I really am lost? I don't get those..
Chris cuts half a rectangular lawn, 40m by 30m by moving strips of equal width around perimeter. Jerri cuts the small rectangle left How wode a strip does Chris cut so that they share equally?

Help!

Suppose the width of strip is x

Then length of inner rectangle = 40 - 2x, width = 30 - 2x

Hence area of inner rectangle = (40 - 2x) (30 - 2x)

total area = 40 times 30 = 1200

Hence area of the stripped part = 1200 - (40 - 2x) (30 - 2x)

The two are equal:

1200 - (40 - 2x) (30 - 2x) = (40 - 2x) (30 - 2x)

Solve this equation to get x