The perimeter of a rectangle and square are 160m each. The area of the rectangle is less than that it’s square by 100cm meters. The less than that of the square by 100 sq.meters. the length of rectangle is___________?

A. 30m
B. 40m
C. 50m
D. 60m
Explanation:
Each side of the square = 160/4m =40 cm
2(l+b) = 160
=> (l+b) = 80 (40) 2 –lb = 100
=> lb =(1600 – 100) = 1500 (l-b) 2 = (l+b) 2 – 4lb
= (80) 2 -4 x 1500 =(6400 -6000) = 400 (l-b) = 20
Therefore, l+b = 80, l-b =20
=> 2l =100
=> l= 50m