The perimeter of a rectangle is 60 cm. The length of the rectangle is four times the width. This
information is shown in the equations below.
2L+ 2w = 60
1L = 4w

You can simply use substitution. Since 1L=4w, what we can do is substitute any Ls for 4w and vice versa.
2L+2w=60
8w+2w=60
10w=60
w=6
Next, we insert w into the equation to find the value of l.
2L+2(6)=60
2L+12=60
2L=48
L=24
We can check our answers by inserting them into the second equation
1(24)=4(6)
24=24
This is true therefore our answer is correct.

The answer is $23.63