The best approach is to divide what you know into smaller more reasonable chunks. This problem requires to equations to solve because you have two variables; length and width. First off what is the formula for the perimeter of a rectangle? Set that equal to 160cm. The next equation comes from the second sentence. Look at the words and decipher where the equal sign is located. Think in terms of length somehow equals width, but how? Once you have your two equations, solve for one of the variables and substitute into the other equation to solve for one of the variables. Take that number and plug it back into the equation to solve for the other variable.

Good luck!

Here’s a hint:

peimeter is 2(a+b), if a and b are length, width

but in this case if width is b, then length is (3b-4)

Now figure the rest out