Question 722993
So write down what you know and draw the rectangle. 
You know that the area is 320cm^2, write that in the middle. 
Then l=5w because length is five times greater than width. 
The formula for area is A=lw so plug in the numbers you have and plug 5w for length. 
You then get 320=(5w)w. You must multiply 5w to w which will give you 5w^2=320. From there you need to divide 5 on both sides. That way you get rid of the 5 on the left and make 320 into 64. Your problem is now w^2=64. To finish this part you need to find the square root of 64 which is 8 and that gives you your width. Now plug 8 for w in 5w and get your length of 40. Using the formula to get your perimeter P=l+l+w+w or P=2(l)+2(w) plug in 40 for length and 8 for width. P=2(40)+2(8). This equals P=80+16 and then P=96. DO NOT FORGET TO LABEL!!!
Here is everything but not so wordy.
l=5w w=? A=320cm^2 P=? A=lw P=2l+2w
{{{320=(5w)w}}} -> {{{320=5w^2}}} -> {{{(320)/(5)=(5w^2)/(5)}}} -> {{{root(2,64)=root(2,w^2)}}} {{{8=w}}} 

l=5(8)=40cm w=8cm A=320cm^2 P=? A=lw P=2l+2w
{{{P=2(40)+2(8)}}} -> {{{P=80+16}}} -> {{{P=96}}}

l=40cm w=8cm A=320cm^2 P=96cm

LABEL!