Question 579088
length = x
width = y

y=x-4..............................(1)

perimeter = 2(L+W)

2(x+y)= 36..........................(2)

substitute y in this equation 
2(x+x-4)=36
2(2x-4)=36
/2
2x-4 = 18
2x=18+4
2x=22
/2
x=11 cm the length 
width = 11-4 = 7cm