10. the perimeter of a parallelogram is 72 meters. the width of the parallelogram is 4 meters less than its length. find the length and the width of the parallelogram.

Let, 
Length = a
Width= b

a-b=4  --eq(1)
since perimeter of parallelogram P=2(a+b)
therefore 
2a+2b=72  --eq(2)

eq(1)=> 
a=b+4

substitute the value of a in eq 2

Eq(2)=>
2(b+4)+2b=72
2b+8+2b=72
4b=72-8
4b=64
b=16

Substitue the value of b in eq(1)

Eq(1)=>
a-16=4
a=20