Answer:
72cm²
Explanation:
perimeter= 2(l+w)
 36 = 2(l+w)
 36/2 = l+w
 18 = l+w
since, l is twice as w
 18= 2w + w
18 = 3w (we can add since all the variables, and exponents are same)
 18/3 = w
6= w
NOW,
 w=6 and l is equal to twice as 6 
so l=12
area= l×b
 = 12×6 = 72cm²
hope this helps. It was toooo long