Question

a rectangular plot of land has a perimeter of 140m and the length 40 m.find its area?

Answer 1

Perimeter= 2(l+b)
=140=2(40+b)
140=80+2b
140-80=2b
60=2b
b=60/2
b=30 m

Area =l×b
40×30
=1200m^2

Answer 2

Perimeter of rectangle=$\red{\boxed{2(l+b)}}$

by using this formula-

P=2(l+b)
140=2(40+b)
70=40+b
30=b

Breadth of rectangle is 30m

$\blue{\boxed{Area\:of\: rectangle\:=l×b}}$

by using this

Area=40×30=1200m^2.