Explanation:
let the length of rectangle be x
let the breadth of rectangle be x - 4m
the perimeter of rectangle=40m
solution,
perimeter of rectangle=40m
2(l+b)=40m
2(x+x-4)=40m
2(2x-4)=40m
4x-8=40m
4x=40+8
or,4x=48
or,x=48/4
•°•, x=12
so,
length of rectangle=x=12
breadth of rectangle=x-4
= 12-4
=8