Arectangular piece of land with length a meters and width 80 m less than its length has the perimeter of 240 m. find the length and width of this land.

The land would be 100x20.
240 is full perimeter. 
width is 80m less than length
80+80=160 (because theres 2 width sides)
240-160=80
80/4(because 4 sides)= 20m for each side
20+80=100
20+80=100
20+0=20
20+0=20
add all the sides together and get 240 meters for the full perimeter

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